Semiconductor memory device

ABSTRACT

According to one embodiment, a semiconductor memory device includes first to nth string units (n being a natural number of 3 or more), a plurality of layers of word lines, and (n−1) layers of select gate layers. The first to nth string units each includes a memory string. The memory string includes a plurality of memory cells and a plurality of select transistors connected in series in a first direction. The (n−1) layers of select gate layers include first to (2×(n−1))th select gates electrically isolated from each other. The first string unit is selected by the first to (n−1)th select gates. The kth string unit (k being not less than 1 and not more than n) is selected by the kth to (n+k−2)th select gates. The nth string unit is selected by the nth to (2×(n−1))th select gates.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority from U.S. application Ser.No. 16/048,912, filed Jul. 30, 2018, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2017-204702,filed on Oct. 23, 2017; the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor memorydevice.

BACKGROUND

A memory device that has a three-dimensional structure including astacked body including multiple layers of conductive layers stacked withan insulator interposed, a semiconductor body provided inside a memoryhole piercing the stacked body, and a charge storage portion providedbetween the semiconductor body and the conductive layers has beenproposed. The multiple layers of conductive layers include multiple wordlines functioning as control gates of memory cells, and select gatesfunctioning as control gates of select transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a semiconductormemory device of an embodiment;

FIG. 2 is a schematic perspective view of the semiconductor memorydevice of the embodiment;

FIG. 3 is a schematic cross-sectional view of the semiconductor memorydevice of the embodiment;

FIG. 4 is an enlarged view of one portion of FIG. 3;

FIG. 5 is a circuit diagram of a semiconductor memory device of a firstembodiment;

FIG. 6 is a schematic cross-sectional view of the semiconductor memorydevice of the first embodiment;

FIGS. 7A to 7C are schematic plan views of the semiconductor memorydevice of the first embodiment;

FIG. 8A to FIG. 11B are schematic cross-sectional views showing a methodfor manufacturing the semiconductor memory device of the firstembodiment;

FIG. 12 is a circuit diagram of the semiconductor memory device of thefirst embodiment;

FIG. 13 is a schematic cross-sectional view of the semiconductor memorydevice of the first embodiment;

FIGS. 14A to 14D are schematic plan views of the semiconductor memorydevice of the first embodiment;

FIG. 15 is a circuit diagram of a semiconductor memory device of asecond embodiment;

FIG. 16 is a schematic cross-sectional view of the semiconductor memorydevice of the second embodiment;

FIG. 17 is a circuit diagram of the semiconductor memory device of thesecond embodiment;

FIG. 18 is a circuit diagram of the semiconductor memory device of thesecond embodiment;

FIG. 19 is a schematic cross-sectional view of the semiconductor memorydevice of the second embodiment;

FIG. 20 is a circuit diagram of the semiconductor memory device of thesecond embodiment;

FIG. 21 is a schematic cross-sectional view of the semiconductor memorydevice of the second embodiment;

FIGS. 22A to 22C are figures illustrating potential controls ofsource-side select gates of the semiconductor memory device of thesecond embodiment;

FIG. 23 is a schematic cross-sectional view of another example of amemory cell array of the embodiment;

FIG. 24 is a circuit diagram of a semiconductor memory device of a thirdembodiment;

FIG. 25 is a circuit diagram of the semiconductor memory device of thethird embodiment;

FIG. 26 is a schematic cross-sectional view of the semiconductor memorydevice of the third embodiment;

FIG. 27 is a circuit diagram of the semiconductor memory device of thethird embodiment;

FIG. 28 is a schematic cross-sectional view of the semiconductor memorydevice of the third embodiment;

FIG. 29 is a circuit diagram of a semiconductor memory device of afourth embodiment;

FIG. 30 is a circuit diagram of the semiconductor memory device of thefourth embodiment;

FIG. 31 is a schematic cross-sectional view of the semiconductor memorydevice of the fourth embodiment;

FIG. 32 is a circuit diagram of the semiconductor memory device of thefourth embodiment;

FIG. 33 is a schematic cross-sectional view of the semiconductor memorydevice of the fourth embodiment;

FIGS. 34A to 34D are figures illustrating potential controls of selectgates of the semiconductor memory devices of the third and fourthembodiments;

FIG. 35A is a drawing illustrating a threshold of a memory cell and anallotment of a data in the case where one bit of data is stored in onememory cell, and FIG. 35B is a waveform diagram of a word line whenreading;

FIG. 36A is a drawing illustrating a threshold of a memory cell and anallotment of a data in the case where two bits of data are stored in onememory cell, and FIGS. 36B and 36C are waveform diagrams of a word linewhen reading in the case where the two bits are stored in the one memorycell;

FIG. 37 is a schematic view showing a chip configuration of asemiconductor memory device of a fifth embodiment;

FIG. 38A is a drawing showing a relationship of thresholds of a memorycell of the fifth embodiment, and FIGS. 38B and 38C are drawings showinga voltage of a word line connected to a gate of a memory cell whenreading in the fifth embodiment;

FIG. 39A is a figure showing a relationship between memory cells and adata that is read in the fifth embodiment, and FIG. 39B is a figureshowing a definition of a data that is read;

FIG. 40 is an explanation drawing of a data program operation in thefifth embodiment;

FIGS. 41A and 41B are drawings showing a voltage of a word lineconnected to a gate of a memory cell when reading in a modification ofthe fifth embodiment;

FIG. 42A is a figure illustrating a relationship between memory cellsand a data that is read in the modification of the fifth embodiment, andFIG. 42B is a figure showing a definition of the data that is read inthe modification of the fifth embodiment;

FIG. 43 is an explanation drawing of a data program operation in themodification of the fifth embodiment;

FIG. 44 is a schematic view showing a chip configuration of thesemiconductor memory device of the fifth embodiment;

FIG. 45 is a circuit diagram of another example of the semiconductormemory device of the first embodiment;

FIG. 46 is a schematic cross-sectional view of the semiconductor memorydevice shown in FIG. 45 of the first embodiment; and

FIGS. 47A and 47B are schematic plan views of the semiconductor memorydevice shown in FIGS. 45 and 46 of the first embodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor memory device includesfirst to nth string units (n being a natural number of 3 or more), aplurality of layers of word lines, and (n−1) layers of select gatelayers. The first to nth string units each includes a memory string. Thememory string includes a plurality of memory cells and a plurality ofselect transistors connected in series in a first direction. The layersof word lines are stacked in the first direction. The (n−1) layers ofselect gate layers are stacked in the first direction. The (n−1) layersof select gate layers include first to (2×(n−1))th select gateselectrically isolated from each other. The first string unit is selectedby the first to (n−1)th select gates. The kth string unit (k being notless than 1 and not more than n) is selected by the kth to (n+k−2)thselect gates. The nth string unit is selected by the nth to (2×(n−1))thselect gates.

Embodiments will now be described with reference to the drawings. Thesame components in the drawings are marked with the same referencenumerals.

FIG. 1 is a block diagram showing the configuration of a semiconductormemory device of an embodiment.

The semiconductor memory device of the embodiment includes a memory cellarray 1 having a three-dimensional structure, and a control circuit 2controlling the memory cell array 1. The control circuit 2 includes arow decoder that controls word lines and select gates described below.

FIG. 2 is a schematic perspective view of the memory cell array 1.

FIG. 3 is a schematic cross-sectional view of the memory cell array 1.

In FIG. 2, two mutually-orthogonal directions parallel to a majorsurface of a substrate 10 are taken as an X-direction and a Y-direction;and a direction orthogonal to both the X-direction and the Y-directionis taken as a Z-direction (a stacking direction).

The memory cell array 1 includes the substrate 10, a source layer (orsource line) SL provided on the substrate 10, a stacked body 100provided on the source layer SL, multiple columnar portions CL, andmultiple bit lines BL provided above the stacked body 100.

The substrate 10 is, for example, a silicon substrate. The source layerSL includes a semiconductor layer doped with an impurity and may furtherinclude a layer including a metal. An insulating layer 41 is providedbetween the substrate 10 and the source layer SL.

The stacked body 100 is divided into multiple blocks 200 by a separationportion 60. The separation portion 60 extends in the stacking direction(the Z-direction) and reaches the source layer SL. Further, theseparation portion 60 extends in the X-direction and divides the stackedbody 100 into the multiple blocks 200 in the Y-direction. For example,an erase operation is executed by block unit.

The separation portion 60 is, for example, an insulating film providedinside a slit piercing the stacked body 100. FIG. 3 illustrates oneblock 200 between two separation portions 60.

The columnar portions CL are formed in substantially circular columnarconfigurations extending through the stacked body 100 in the stackingdirection (the Z-direction). The columnar portions CL pierce the stackedbody 100 and reach the source layer SL. For example, the multiplecolumnar portions CL have a staggered arrangement. Or, the multiplecolumnar portions CL may be arranged in a square lattice along theX-direction and the Y-direction.

As shown in FIG. 2, the multiple bit lines BL are metal films extendingin the Y-direction. The multiple bit lines BL are separated from eachother in the X-direction. The upper end portions of semiconductor bodies20 of the columnar portions CL described below are connected to the bitlines BL via contacts Cb and V1.

As shown in FIG. 3, the stacked body 100 is provided on the source layerSL. The stacked body 100 includes multiple conductive layers 70 stackedin a direction (the Z-direction) perpendicular to the major surface ofthe substrate 10 with insulating layers 72 interposed. The conductivelayers 70 are, for example, metal layers. The insulating layer 72 isprovided also between the source layer SL and the conductive layer 70 ofthe lowermost layer. A gap may be used as the insulator between theconductive layers 70.

FIG. 4 is an enlarged view of one portion of FIG. 3.

The columnar portion CL includes a memory film 30, the semiconductorbody 20, and an insulative core film 50. The semiconductor body 20 isformed in a pipe-like configuration;

and the core film 50 is provided on the inner side of the semiconductorbody 20. The memory film 30 is provided between the semiconductor body20 and the conductive layers 70 and surrounds the periphery of thesemiconductor body 20.

The semiconductor body 20 is, for example, a silicon film; and the lowerend portion of the semiconductor body 20 contacts the source layer SL asshown in FIG. 3. The upper end portion of the semiconductor body 20 isconnected to the bit line BL via the contacts Cb and V1 shown in FIG. 2.

Or, as shown in FIG. 23, the lower end portion of the semiconductor body20 may contact an active region (e.g., a P-type well) 10 a of thesubstrate 10. In such a case, an interconnect portion LI of a conductivematerial is provided in the separation portion 60 (a slit ST); and thelower end portion of the interconnect portion LI is caused to contact anN⁺-type semiconductor region 81 formed in the active region 10 a of thesubstrate 10. The semiconductor body 20 is connected via a channelformed in the active region 10 a, the N⁺-type semiconductor region 81,and the interconnect portion LI to an upper layer interconnect (a sourceline) provided above the stacked body 100. In the example shown in FIG.23, an insulating layer 42 is provided on the conductive layer 70 of theuppermost layer; and an insulating layer 43 is provided on theinsulating layer 42. The insulating layer 43 covers the upper ends ofthe columnar portions CL.

As shown in FIG. 4, the memory film 30 is a stacked film including atunneling insulating film 31, a charge storage film (a charge storageportion) 32, and a blocking insulating film 33. The blocking insulatingfilm 33, the charge storage film 32, and the tunneling insulating film31 are provided in order from the conductive layer 70 side between thesemiconductor body 20 and the conductive layers 70.

The semiconductor body 20, the memory film 30, and the conductive layer70 are included in a memory cell MC. The multiple conductive layers 70include multiple word lines WL functioning as control gates of thememory cells MC. The memory cell MC has a vertical transistor structurein which the word line WL surrounds the periphery of the semiconductorbody 20 with the memory film 30 interposed. In the memory cell MC havingthe vertical transistor structure, the semiconductor body 20 functionsas a channel; and the charge storage film 32 functions as a data storagelayer that stores charge injected from the semiconductor body 20.

The semiconductor memory device of the embodiment is a nonvolatilesemiconductor memory device that can freely and electricallyerase/program data and can retain the memory content even when the powersupply is OFF.

The memory cell MC is, for example, a charge trap memory cell. Thecharge storage film 32 has many trap sites that trap charge inside aninsulative film and includes, for example, a silicon nitride film. Or,the charge storage film 32 may be a conductive floating gate surroundedwith an insulator.

The tunneling insulating film 31 is used as a potential barrier when thecharge is injected from the semiconductor body 20 into the chargestorage film 32 or when the charge stored in the charge storage film 32is discharged into the semiconductor body 20. The tunneling insulatingfilm 31 includes, for example, a silicon oxide film.

The blocking insulating film 33 prevents the charge stored in the chargestorage film 32 from being discharged into the word line WL. Also, theblocking insulating film 33 prevents back-tunneling of the charge fromthe word line WL into the columnar portion CL.

The blocking insulating film 33 includes, for example, a silicon oxidefilm. Or, the blocking insulating film 33 may be, for example, a stackedfilm of a silicon oxide film and a metal oxide film. In the stackedfilm, the silicon oxide film is provided between the charge storage film32 and the metal oxide film; and the metal oxide film is providedbetween the silicon oxide film and the word line WL.

As shown in FIG. 2, a drain-side select transistor STD is provided inthe upper layer portion of the stacked body 100; and a source-sideselect transistor STS is provided in the lower layer portion of thestacked body 100.

The conductive layer 70 of at least the uppermost layer of the multipleconductive layers 70 functions as a control gate (a drain-side selectgate) of the drain-side select transistor STD; and the conductive layer70 of at least the lowermost layer of the multiple conductive layers 70functions as a control gate (a source-side select gate) of thesource-side select transistor STS.

The semiconductor body 20 pierces the multiple conductive layers 70including the word lines WL and the select gates. The memory film 30shown in FIG. 4 is provided also between the semiconductor body 20 andthe conductive layer used as the drain-side select gate and between thesemiconductor body 20 and the conductive layer 70 used as thesource-side select gate.

The multiple memory cells MC are provided between the drain-side selecttransistor STD and the source-side select transistor STS. The multiplememory cells MC, the drain-side select transistor STD, and thesource-side select transistor STS are connected in series via thesemiconductor body 20 (the channel) and are included in one memorystring MS. For example, the memory strings MS have a staggeredarrangement in planar directions parallel to the XY plane; and themultiple memory cells MC are provided three-dimensionally in theX-direction, the Y-direction, and the Z-direction.

FIG. 5 is a circuit diagram of the semiconductor memory device of thefirst embodiment.

FIG. 6 is a schematic cross-sectional view of the semiconductor memorydevice of the first embodiment. FIG. 6 is a cross-sectional view of aportion of the one block 200 separated from the other blocks by theseparation portions 60 described above where the memory cells MC and thedrain-side select transistors are provided.

In the example shown in FIG. 6, three string units SU0, SU1, and SU2 aredisposed in the one block 200. One string unit includes multiple memorystrings MS (multiple columnar portions CL).

In the example shown in FIG. 6, two layers of the drain-side select gatelayers are stacked in the upper layer portion of the stacked body 100.The insulating layer 72 is provided between the two layers of thedrain-side select gate layers.

The drain-side select gate layer of the uppermost layer is divided intotwo select gates in the Y-direction by a separation portion 62 a. Theseparation portion 62 a divides the drain-side select gate layer of theuppermost layer into a first drain-side select gate SGD0A and a thirddrain-side select gate SGD0B.

The drain-side select gate layer of the second layer from the top isdivided into two select gates in the Y-direction by a separation portion62 b. The separation portion 62 b divides the drain-side select gatelayer of the second layer from the top into a second drain-side selectgate SGD1A and a fourth drain-side select gate SGD1B.

The first drain-side select gate SGD0A, the second drain-side selectgate SGD1A, the third drain-side select gate SGD0B, and the fourthdrain-side select gate SGD1B each are controlled electricallyindependently.

FIG. 7A is a schematic plan view of the layer of the one block 200 wherethe first drain-side select gate SGD0A and the third drain-side selectgate SGD0B are provided.

FIG. 7B is a schematic plan view of the layer of the one block 200 wherethe second drain-side select gate SGD1A and the fourth drain-side selectgate SGD1B are provided.

FIG. 7C is a schematic plan view of the layer of the one block 200 wherethe word line WL is provided.

The word line WL of each layer is provided commonly for the first tothird string units SU0 to SU2. The first drain-side select gate SGD0A isprovided in the first string unit SU0. The third drain-side select gateSGD0B is provided commonly for the second string unit SU1 and the thirdstring unit SU2. The second drain-side select gate SGD1A is providedcommonly for the first string unit SU0 and the second string unit SU1.The fourth drain-side select gate SGD0B is provided in the third stringunit SU2.

The separation portion 62 a and the separation portion 62 b areinsulating films that extend in the same direction as the separationportion 60 (the slit ST).

As shown in FIG. 6, the three string units SU0, SU1, and SU2 in the oneblock 200 are arranged to be separated from each other in theY-direction.

The separation portion 62 a is disposed between the first string unitSU0 and the second string unit SU1 adjacent to each other in theY-direction, pierces only the drain-side select gate layer of theuppermost layer of the multiple conductive layers 70, and does notdivide the other conductive layers of the multiple conductive layers 70.

The separation portion 62 b is disposed between the second string unitSU1 and the third string unit SU2 adjacent to each other in theY-direction, pierces only the drain-side select gate layer of the secondlayer from the top of the multiple conductive layers 70, and does notdivide the other conductive layers of the multiple conductive layers 70.

As shown in FIG. 6, FIG. 7A, and FIG. 7B, the position in theY-direction of the separation portion 62 a provided in the drain-sideselect gate layer of the uppermost layer and the position in theY-direction of the separation portion 62 b provided in the drain-sideselect gate layer of the second layer from the top are shifted from eachother.

As shown in FIG. 5, the first string unit SU0 includes a firstdrain-side select transistor STD0A having the first drain-side selectgate SGD0A as a control gate and a second drain-side select transistorSTD1A having the second drain-side select gate SGD1A as a control gate.

The second string unit SU1 includes a third drain-side select transistorSTD0B having the third drain-side select gate SGD0B as a control gateand the second drain-side select transistor STD1A having the seconddrain-side select gate SGD1A as a control gate.

The third string unit SU2 includes the third drain-side selecttransistor STD0B having the third drain-side select gate SGD0B as acontrol gate and a fourth drain-side select transistor STD1B having thefourth drain-side select gate SGD1B as a control gate.

Any one of the string units of the three string units SU0, SU1, and SU2inside the one block 200 is selected by the drain-side selecttransistors STD0A, STD0B, STD1A, and STD1B.

When the first string unit SU0 is selected, a potential that is thethreshold voltage or more is applied to the first drain-side select gateSGD0A and the second drain-side select gate SGD1A; and the firstdrain-side select transistor STD0A and the second drain-side selecttransistor STD1A are set to ON. The third drain-side select transistorSTD0B and the fourth drain-side select transistor STD1B are set to OFF.

The semiconductor bodies 20 of the selected first string unit SU0 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected second string unit SU1 and the semiconductor bodies20 of the unselected third string unit SU2 are not electricallyconnected to the bit lines BL.

When the second string unit SU1 is selected, a potential that is thethreshold voltage or more is applied to the third drain-side select gateSGD0B and the second drain-side select gate SGD1A; and the thirddrain-side select transistor STD0B and the second drain-side selecttransistor STD1A are set to ON. The first drain-side select transistorSTD0A and the fourth drain-side select transistor STD1B are set to OFF.

The semiconductor bodies 20 of the selected second string unit SU1 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected first string unit SU0 and the semiconductor bodies20 of the unselected third string unit SU2 are not electricallyconnected to the bit lines BL.

When the third string unit SU2 is selected, a potential that is thethreshold voltage or more is applied to the third drain-side select gateSGD0B and the fourth drain-side select gate SGD1B; and the thirddrain-side select transistor STD0B and the fourth drain-side selecttransistor STD0B are set to ON. The first drain-side select transistorSTD0A and the second drain-side select transistor STD0A are set to OFF.

The semiconductor bodies 20 of the selected third string unit SU2 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected first string unit SU0 and the semiconductor bodies20 of the unselected second string unit SU1 are not electricallyconnected to the bit lines BL.

A method for manufacturing the semiconductor memory device of the firstembodiment will now be described with reference to FIG. 8A to FIG. 11B.

As shown in FIG. 8A, the insulating layer 41 is formed on the substrate10; the source layer SL is formed on the insulating layer 41; and thestacked body 100 is formed on the source layer SL. The substrate 10, theinsulating layer 41, and the source layer SL are not illustrated in FIG.8B to FIG. 11B.

The insulating layer 72 and a sacrificial layer 71 are stackedalternately on the source layer SL. The process of alternately stackingthe insulating layer 72 and the sacrificial layer 71 is repeated; andthe stacked body 100 that includes the multiple insulating layers 72 andthe multiple sacrificial layers 71 is formed on the source layer SL. Forexample, the insulating layers 72 are silicon oxide layers; and thesacrificial layers 71 are silicon nitride layers.

As shown in FIG. 8B, a mask (e.g., a silicon oxide film) 75 is formed onthe stacked body 100; and a slit 61 b is formed by RIE (reactive ionetching). The slit 61 b pierces the mask 75, the insulating layer 72 ofthe uppermost layer, and the sacrificial layer 71 of the uppermostlayer. The bottom surface of the slit 61 b is positioned in theinsulating layer 72 of the second layer from the top.

As shown in FIG. 8C, the separation portion 62 b is formed inside theslit 61 b by filling an insulating film (e.g., a silicon oxide film) 62.The insulating film 62 is deposited also on the mask 75. For example,the mask 75 and the insulating film 62 deposited on the mask 75 areremoved by etch-back (FIG. 9A). The sacrificial layer 71 of theuppermost layer is divided by the separation portion 62 b of a materialthat is different from that of the sacrificial layers 71.

Subsequently, as shown in FIG. 9B, one layer of the sacrificial layers71, one layer of the insulating layers 72, and a mask (e.g., a siliconoxide film) 76 are stacked in order; and a slit 61 a is formed in thestacked body 100 by using RIE. The slit 61 a is formed at a positionthat is different from the position of the separation portion 62 b.

The slit 61 a pierces the mask 76, the insulating layer 72 of theuppermost layer, and the sacrificial layer 71 of the uppermost layer ofthe stacked body 100 shown in FIG. 9B. The bottom surface of the slit 61a is positioned in the insulating layer 72 of the second layer from thetop.

As shown in FIG. 9C, the separation portion 62 a is formed inside theslit 61 a by filling the insulating film 62. The insulating film 62 isdeposited also on the mask 76. The mask 76 and the insulating film 62deposited on the mask 76 are removed by, for example, etch-back (FIG.10A). The separation portion 62 a is, for example, a silicon oxide filmand divides the sacrificial layer 71 of the uppermost layer.

Subsequently, for example, multiple memory holes are formed in thestacked body 100 by using RIE; and the columnar portions CL are formedinside the memory holes as shown in FIG. 10B. The memory holes piercethe stacked body 100 and reach the source layer SL; and the lower endportions of the semiconductor bodies 20 that are formed inside thememory holes contact the source layer SL.

After forming the columnar portions CL, the slits ST are formed in thestacked body 100 as shown in FIG. 11A. The slits ST are formed by RIEusing a not-illustrated mask, pierce the stacked body 100, and reach thesource layer SL.

Then, the sacrificial layers 71 are removed by etching via the slits ST.For example, the sacrificial layers 71 which are silicon nitride layersare removed using a solution including phosphoric acid. The separationportions 62 a and 62 b which are silicon oxide films are not removed.

The sacrificial layers 71 are removed; and a gap 73 is formed betweenthe multiple insulating layers 72 as shown in FIG. 11A. The multipleinsulating layers 72 contact the side surfaces of the multiple columnarportions CL to surround the side surfaces. The multiple insulatinglayers 72 are supported by such a physical bond with the multiplecolumnar portions CL; and the gap 73 is maintained.

As shown in FIG. 11B, the conductive layers that are used to form theselect gates SGD0A, SGD0B, SGD1A, and SGD0B and the word lines WL areformed inside the gap 73. For example, a tungsten layer is formed by CVD(chemical vapor deposition) as the conductive layers. A film formationgas is supplied to the gap 73 via the slits ST. Or, the separationportions 62 a and 62 b (the slits 61 a and 61 b) also can be formedafter forming the conductive layers 70 (after the replacement).

Generally, there is a tendency for the width of a slit formed by RIE toincrease as the depth increases. According to the embodiment, the depthsof the separation portions 62 a and 62 b (the slits 61 a and 61 b)dividing the drain-side select gate layers formed in the upper layerportion of the stacked body 100 are shallower than the depths of theseparation portions 60 (the slits ST) dividing the entire stacked body100. Therefore, the widths of the separation portions 62 a and 62 b (theslits 61 a and 61 b) are narrower than the widths of the separationportions 60.

Here, as a comparative example, a configuration may be used in which theseparation portion 60 (the slit ST) that pierces the entire stacked body100 divides the drain-side select gate layer of the second string unitSU1 and the drain-side select gate layer of the third string unit SU2.

Conversely, according to the embodiment, the separation portion 62 bthat has a smaller width than the separation portion 60 (the slit ST)divides the drain-side select gate layer of the second string unit SU1and the drain-side select gate layer of the third string unit SU2.Therefore, according to the embodiment, it is possible to reduce thenumber of the separation portions 60 (the slits ST) and reduce theplanar size of the memory cell array.

The separation portion 62 a and the separation portion 62 b dividedrain-side select gate layers of different layers and are disposed atpositions that are shifted from each other in the Y-direction. Theseparation portion 62 a is disposed between the first string unit SU0and the second string unit SU1; and the separation portion 62 b isdisposed between the second string unit SU1 and the third string unitSU2.

Accordingly, when the sacrificial layers 71 are replaced with theconductive layers 70 via the slits ST as shown in FIGS. 11A and 11B, thetwo regions that are divided in the Y-direction by the separationportion 62 a (the regions where the drain-side select gate SGD0A and thedrain-side select gate SGD0B are formed) each communicate with the slitST; and the two regions that are divided in the Y-direction by theseparation portion 62 b (the regions where the drain-side select gateSGD1A and the drain-side select gate SGD0B are formed) each communicatewith the slit ST.

Accordingly, the replacement of the sacrificial layer 71 with theconductive layer used to form the drain-side select gate layer can beperformed even for the region where the second string unit SU1 notadjacent to the slit ST is disposed.

Another example of the semiconductor memory device of the firstembodiment will now be described with reference to FIG. 12 to FIG. 14D.

FIG. 12 is a circuit diagram of the other example of the semiconductormemory device of the first embodiment.

FIG. 13 is a schematic cross-sectional view of the other example of thesemiconductor memory device of the first embodiment.

In the example shown in FIGS. 12 and 13, the four string units SU0, SU1,SU2, and SU3 are disposed in one block 200. Also, three layers of thedrain-side select gate layers are stacked in the upper layer portion ofthe stacked body 100. The insulating layers 72 are provided between thedrain-side select gate layers.

The drain-side select gate layer of the uppermost layer is divided intotwo select gates in the Y-direction by the separation portion 62 a. Theseparation portion 62 a divides the drain-side select gate layer of theuppermost layer into the first drain-side select gate SGD0A and thefourth drain-side select gate SGD0B.

The drain-side select gate layer of the second layer from the top isdivided into two select gates in the Y-direction by the separationportion 62 b. The separation portion 62 b divides the drain-side selectgate layer of the second layer from the top into the second drain-sideselect gate SGD1A and a fifth drain-side select gate SGD1B.

The drain-side select gate layer of the third layer from the top isdivided into two select gates in the Y-direction by a separation portion62 c. The separation portion 62 c divides the drain-side select gatelayer of the third layer from the top into a third drain-side selectgate SGD2A and a sixth drain-side select gate SGD2B.

The first drain-side select gate SGD0A, the second drain-side selectgate SGD1A, the third drain-side select gate SGD2A, the fourthdrain-side select gate SGD0B, the fifth drain-side select gate SGD1B,and the sixth drain-side select gate SGD2B each are controlledelectrically independently.

FIG. 14A is a schematic plan view of the layer of the one block 200where the first drain-side select gate SGD0A and the fourth drain-sideselect gate SGD0B are provided.

FIG. 14B is a schematic plan view of the layer of the one block 200where the second drain-side select gate SGD1A and the fifth drain-sideselect gate SGD1B are provided.

FIG. 14C is a schematic plan view of the layer of the one block 200where the third drain-side select gate SGD2A and the sixth drain-sideselect gate SGD2B are provided.

FIG. 14D is a schematic plan view of the layer of the one block 200where the word line WL is provided.

The word line WL of each layer is provided commonly for the first tofourth string units SU0 to SU3. The fourth drain-side select gate SGD0Bis provided commonly for the second string unit SU1, the third stringunit SU2, and the fourth string unit SU3. The second drain-side selectgate SGD1A is provided commonly for the first string unit SU0 and thesecond string unit SU1. The fifth drain-side select gate SGD1B isprovided commonly for the third string unit SU2 and the fourth stringunit SU3. The third drain-side select gate SGD2A is provided commonlyfor the first string unit SU0, the second string unit SU1, and the thirdstring unit SU2.

The separation portions 62 a to 62 c are insulating films extending inthe same direction as the separation portions 60 (the slits ST) piercingthe entire stacked body 100.

As shown in FIG. 13, the four string units SU0, SU1, SU2, and SU3 of theone block 200 are arranged to be separated from each other in theY-direction.

The separation portion 62 a is disposed between the first string unitSU0 and the second string unit SU1 adjacent to each other in theY-direction, pierces only the drain-side select gate layer of theuppermost layer of the multiple conductive layers 70, and does notdivide the other conductive layers of the multiple conductive layers 70.

The separation portion 62 b is disposed between the second string unitSU1 and the third string unit SU2 adjacent to each other in theY-direction, pierces only the drain-side select gate layer of the secondlayer from the top of the multiple conductive layers 70, and does notdivide the other conductive layers.

The separation portion 62 c is disposed between the third string unitSU2 and the fourth string unit SU3 adjacent to each other in theY-direction, pierces only the drain-side select gate layer of the thirdlayer from the top of the multiple conductive layers 70, and does notdivide the other conductive layers.

As shown in FIG. 13 and FIGS. 14A to 14D, the position in theY-direction of the separation portion 62 a provided in the drain-sideselect gate layer of the uppermost layer, the position in theY-direction of the separation portion 62 b provided in the drain-sideselect gate layer of the second layer from the top, and the position inthe Y-direction of the separation portion 62 c provided in thedrain-side select gate layer of the third layer from the top are shiftedfrom each other.

As shown in FIG. 12, the first string unit SU0 includes the firstdrain-side select transistor STD0A having the first drain-side selectgate SGD0A as a control gate, the second drain-side select transistorSTD1A having the second drain-side select gate SGD1A as a control gate,and a third drain-side select transistor STD2A having the thirddrain-side select gate SGD2A as a control gate.

The second string unit SU1 includes a fourth drain-side selecttransistor STD0B having the fourth drain-side select gate SGD0B as acontrol gate, the second drain-side select transistor STD1A having thesecond drain-side select gate SGD1A as a control gate, and the thirddrain-side select transistor STD2A having the third drain-side selectgate SGD2A as a control gate.

The third string unit SU2 includes the fourth drain-side selecttransistor having the fourth drain-side select gate SGD0B as a controlgate, the fifth drain-side select transistor having the fifth drain-sideselect gate SGD1B as a control gate, and the third drain-side selecttransistor having the third drain-side select gate SGD2A as a controlgate.

The fourth string unit SU3 includes the fourth drain-side selecttransistor having the fourth drain-side select gate SGD0B as a controlgate, the fifth drain-side select transistor having the fifth drain-sideselect gate SGD1B as a control gate, and the sixth drain-side selecttransistor having the sixth drain-side select gate SGD2B as a controlgate.

Any one of the string units of the four string units SU0, SU1, SU2, andSU3 inside the one block 200 is selected by the drain-side selecttransistors.

When the first string unit SU0 is selected, a potential that is thethreshold voltage or more is applied to the first drain-side select gateSGD0A, the second drain-side select gate SGD1A, and the third drain-sideselect gate SGD2A; and the first drain-side select transistor, thesecond drain-side select transistor, and the third drain-side selecttransistor are set to ON. The fourth drain-side select transistor, thefifth drain-side select transistor, and the sixth drain-side selecttransistor are set to OFF.

The semiconductor bodies 20 of the selected first string unit SU0 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected second to fourth string units SU1 to SU3 are notelectrically connected to the bit lines BL.

When the second string unit SU1 is selected, a potential that is thethreshold voltage or more is applied to the fourth drain-side selectgate SGD0B, the second drain-side select gate SGD1A, and the thirddrain-side select gate SGD2A; and the fourth drain-side selecttransistor, the second drain-side select transistor, and the thirddrain-side select transistor are set to ON. The first drain-side selecttransistor, the fifth drain-side select transistor, and the sixthdrain-side select transistor are set to OFF.

The semiconductor bodies 20 of the selected second string unit SU1 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected first, third, and fourth string units SU0, SU2, andSU3 are not electrically connected to the bit lines BL.

When the third string unit SU2 is selected, a potential that is thethreshold voltage or more is applied to the fourth drain-side selectgate SGD0B, the fifth drain-side select gate SGD0B, and the thirddrain-side select gate SGD2A; and the fourth drain-side selecttransistor, the fifth drain-side select transistor, and the thirddrain-side select transistor are set to ON. The first drain-side selecttransistor, the second drain-side select transistor, and the sixthdrain-side select transistor are set to OFF.

The semiconductor bodies 20 of the selected third string unit SU2 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected first, second, and fourth string units SU0, SU1,and SU3 are not electrically connected to the bit lines BL.

When the fourth string unit SU3 is selected, a potential that is thethreshold voltage or more is applied to the fourth drain-side selectgate SGD0B, the fifth drain-side select gate SGD1B, and the sixthdrain-side select gate SGD2B; and the fourth drain-side selecttransistor, the fifth drain-side select transistor, and the sixthdrain-side select transistor are set to ON. The first drain-side selecttransistor, the second drain-side select transistor, and the thirddrain-side select transistor are set to OFF.

The semiconductor bodies 20 of the selected fourth string unit SU3 areelectrically connected to the bit lines BL; and the semiconductor bodies20 of the unselected first to third string units SU0 to SU2 are notelectrically connected to the bit lines BL.

In the example shown in FIG. 13 and FIGS. 14A to 14D as well, it ispossible to reduce the number of the separation portions 60 (the slitsST) having wide widths piercing the entire stacked body 100 and reducethe planar size of the memory cell array.

The separation portions 62 a to 62 c divide drain-side select gatelayers of different layers and are disposed at positions that areshifted from each other in the Y-direction. Accordingly, when replacingthe sacrificial layers 71 with the conductive layers 70 via the slit ST,the two regions divided in the Y-direction by the separation portion 62a (the regions where the drain-side select gate SGD0A and the drain-sideselect gate SGD0B are formed) each communicate with the slit ST; the tworegions divided in the Y-direction by the separation portion 62 b (theregions where the drain-side select gate SGD0A and the drain-side selectgate SGD1B are formed) each communicate with the slit ST; and the tworegions divided in the Y-direction by the separation portion 62 c (theregions where the drain-side select gate SGD2A and the drain-side selectgate SGD2B are formed) each communicate with the slit ST.

Accordingly, the replacement of the sacrificial layers 71 with theconductive layers that are used to form the drain-side select gatelayers can be performed even for the regions where the second stringunit SU1 and the third string unit SU2 that are not adjacent to the slitST are disposed.

The number of string units disposed inside one block 200 subdivided bythe separation portions 60 (the slits ST) may be 5 or more. The numberof string units and the number of layers of drain-side select gatelayers can be specified as follows.

Namely, the semiconductor memory device of the first embodiment includesthe first to nth string units (n being a natural number of 3 or more)including the multiple memory strings MS, and the (n−1) layers of thedrain-side select gate layers stacked in the Z-direction. The (n−1)layers of the drain-side select gate layers include the first to(2×(n−1))th drain-side select gates that are electrically isolated. Thefirst string unit is selected by the first to (n−1)th drain-side selectgates; the second string unit is selected by the second to (n−1+1)thdrain-side select gates; the kth string unit (k being not less than 1and not more than n) is selected by the kth to (n+k−2)th select gates;and the nth string unit is selected by the nth to (2×(n−1))th drain-sideselect gates.

A semiconductor memory device of a second embodiment will now bedescribed.

FIG. 15 is a circuit diagram of the semiconductor memory device of thesecond embodiment.

FIG. 16 is a schematic cross-sectional view of the semiconductor memorydevice of the second embodiment.

FIG. 16 shows two sub-blocks 200 a and 200 b subdivided by threeseparation portions 60 (slits ST) separated from each other in theY-direction.

One block which is the erasing unit includes the two sub-blocks 200 aand 200 b; the first string unit SU0 and the second string unit SU1 aredisposed in one sub-block 200 a of the two sub-blocks 200 a and 200 b(on the left side in FIG. 16); and the third string unit SU2 and thefourth string unit SU3 are disposed in the other sub-block 200 b (on theright side in FIG. 16).

Similarly to the first embodiment described above, the multipleconductive layers 70 are stacked on the source layer SL with theinsulating layers 72 interposed. The multiple conductive layers 70include the multiple word lines WL, a drain-side select gate layer, andmultiple layers of the source-side select gate layers.

The word line WL of each layer in the one sub-block 200 a is providedcommonly for the first string unit SU0 and the second string unit SU1.The word line WL of each layer in the other sub-block 200 b is providedcommonly for the third string unit SU2 and the fourth string unit SU3.

In the example shown in FIG. 16, one layer of the drain-side select gatelayers and three layers of the source-side select gate layers areprovided. The multiple layers of the word lines WL are stacked betweenthe drain-side select gate layer and the source-side select gate layers.The three layers of the source-side select gate layers are stackedbetween the source layer SL and the word line WL of the lowermost layer.

In each of the sub-blocks 200 a and 200 b, the drain-side select gatelayer is divided into two select gates in the Y-direction by theseparation portion 62 a. The separation portion 62 a of the onesub-block 200 a divides the drain-side select gate layer into a firstdrain-side select gate SGD0 and a second drain-side select gate SGD1.The separation portion 62 a of the other sub-block 200 b divides thedrain-side select gate layer into a third drain-side select gate SGD2and a fourth drain-side select gate SGD3. The separation portion 62 a isan insulating film extending in the same direction as the separationportions 60 (the slits ST) piercing the entire stacked body 100.

The first to fourth drain-side select gates SGD0 to SGD3 each arecontrolled electrically independently.

The first string unit SU0 and the second string unit SU1 in the onesub-block 200 a are arranged to be separated from each other in theY-direction. The third string unit SU2 and the fourth string unit SU3 inthe other sub-block 200 b are arranged to be separated from each otherin the Y-direction.

As shown in FIG. 15, the memory string of the first string unit SU0includes a first drain-side select transistor STD0 having the firstdrain-side select gate SGD0 as a control gate.

The memory string of the second string unit SU1 includes a seconddrain-side select transistor STD1 having the second drain-side selectgate SGD1 as a control gate.

The memory string of the third string unit SU2 includes a thirddrain-side select transistor STD2 having the third drain-side selectgate SGD2 as a control gate.

The memory string of the fourth string unit SU3 includes a fourthdrain-side select transistor STD3 having the fourth drain-side selectgate SGD3 as a control gate.

As shown in FIG. 16, a first source-side select gate SGS0A, a secondsource-side select gate SGS1A, and a bottom select gate SGSB areprovided in the one sub-block 200 a. The select gates SGS0A, SGS1A, andSGSB are provided commonly for the first string unit SU0 and the secondstring unit SU1.

The bottom select gate SGSB is provided on the source layer SL; thesecond source-side select gate SGS1A is provided on the bottom selectgate SGSB; and the first source-side select gate SGS0A is provided onthe second source-side select gate SGS1A.

The insulating layer 72 is provided between the bottom select gate SGSBand the source layer SL, between the second source-side select gateSGS1A and the bottom select gate SGSB, and between the first source-sideselect gate SGS0A and the second source-side select gate SGS1A.

A first source-side select gate SGS0B, a second source-side select gateSGS1B, and the bottom select gate SGSB are provided in the othersub-block 200 b. The select gates SGS0B, SGS1B, and SGSB are providedcommonly for the third string unit SU2 and the fourth string unit SU3.

The bottom select gate SGSB is provided on the source layer SL; thesecond source-side select gate SGS1B is provided on the bottom selectgate SGSB; and the first source-side select gate SGS0B is provided onthe second source-side select gate SGS1B.

The insulating layer 72 is provided between the bottom select gate SGSBand the source layer SL, between the second source-side select gateSGS1B and the bottom select gate SGSB, and between the first source-sideselect gate SGS0B and the second source-side select gate SGS1B.

The source-side select gate SGS0A and the source-side select gate SGS0Bare provided in the same layer and are divided in the Y-direction by theseparation portions 60 (the slits ST). The source-side select gate SGS1Aand the source-side select gate SGS1B are provided in the same layer,and are divided in the Y-direction by the separation portions 60 (theslits ST).

As shown in FIG. 15, the memory string of the first string unit SU0includes a first source-side select transistor STS0A having the firstsource-side select gate SGS0A as a control gate, a second source-sideselect transistor STS1A having the second source-side select gate SGS1Aas a control gate, and a bottom select transistor STSB having the bottomselect gate SGSB as a control gate.

In one memory string of the first string unit SU0, the first source-sideselect transistor STS0A, the second source-side select transistor STS1A,and the bottom select transistor STSB are connected in series betweenthe source layer SL and the memory cells MC.

The memory string of the second string unit SU1 includes the firstsource-side select transistor STS0A having the first source-side selectgate SGS0A as a control gate, the second source-side select transistorSTS1A having the second source-side select gate SGS1A as a control gate,and the bottom select transistor STSB having the bottom select gate SGSBas a control gate.

In one memory string of the second string unit SU1, the firstsource-side select transistor STS0A, the second source-side selecttransistor STS1A, and the bottom select transistor STSB are connected inseries between the source layer SL and the memory cells MC.

The first source-side select transistor STS0A of the first string unitSU0 is a transistor of the depletion type; and the first source-sideselect transistor STS0A of the second string unit SU1 is a transistor ofthe enhancement type.

Here, the transistor of the depletion type has a negative thresholdvoltage; and the transistor of the enhancement type has a positivethreshold voltage.

The second source-side select transistor STS1A of the first string unitSU0 is a transistor of the enhancement type; and the second source-sideselect transistor STS1A of the second string unit SU1 is a transistor ofthe depletion type.

The memory string of the third string unit SU2 of the other sub-block200 b includes a first source-side select transistor STS0B having thefirst source-side select gate SGS0B as a control gate, a secondsource-side select transistor STS1B having the second source-side selectgate SGS1B as a control gate, and the bottom select transistor STSBhaving the bottom select gate SGSB as a control gate.

In one memory string of the third string unit SU2, the first source-sideselect transistor STS0B, the second source-side select transistor STS1B,and the bottom select transistor STSB are connected in series betweenthe source layer SL and the memory cells MC.

The memory string of the fourth string unit SU3 includes the firstsource-side select transistor STS0B having the first source-side selectgate SGS0B as a control gate, the second source-side select transistorSTS1B having the second source-side select gate SGS1B as a control gate,and the bottom select transistor STSB having the bottom select gate SGSBas a control gate.

In one memory string of the fourth string unit SU3, the firstsource-side select transistor STS0B, the second source-side selecttransistor STS1B, and the bottom select transistor STSB are connected inseries between the source layer SL and the memory cells MC.

The first source-side select transistor STS0B of the third string unitSU2 is a transistor of the depletion type; and the first source-sideselect transistor STS0B of the fourth string unit SU3 is a transistor ofthe enhancement type.

The second source-side select transistor STS1B of the third string unitSU2 is a transistor of the enhancement type; and the second source-sideselect transistor STS1B of the fourth string unit SU3 is a transistor ofthe depletion type. FIG. 22A is a figure (a table) illustrating thepotential controls of the source-side select gates of the semiconductormemory device shown in FIG. 15 and FIG. 16.

In FIG. 22A, “L” and “H” illustrate the potentials applied to thesource-side select gates; and the “L” level (a first level) is apotential that is higher than the threshold voltage of the transistor ofthe depletion type and lower than the threshold voltage of thetransistor of the enhancement type. The “L” level is, for example, 0 V.The “H” level (a second level) is a positive potential that is higherthan the threshold voltage of the transistor of the enhancement type.

Any one of the string units of the first string unit SU0 and the secondstring unit SU1 inside one of the sub-blocks 200 a and 200 b is selectedby the source-side select transistors STS0A, STS1A, and STSB.

When the first string unit SU0 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the firstsource-side select gate SGS0A; the first source-side select transistorSTS0A of the first string unit SU0 is set to ON; the “H” level isapplied to the second source-side select gate SGS1A; and the secondsource-side select transistor STS1A of the first string unit SU0 also isset to ON.

The semiconductor bodies 20 of the selected first string unit SU0 areelectrically connected to the source layer SL.

The first source-side select transistor STS0A of the second string unitSU1 that shares the first source-side select gate SGS0A with the firststring unit SU0 is set to OFF by the “L” level applied to the firstsource-side select gate SGS0A. Accordingly, the semiconductor bodies 20of the unselected second string unit SU1 are not electrically connectedto the source layer SL.

In the other sub-block 200 b, the “L” level is applied to the firstsource-side select gate SGS0B and the second source-side select gateSGS0B; the second source-side select transistor STS1B of the thirdstring unit SU2 are set to OFF; and the first source-side selecttransistor STS0B of the fourth string unit SU3 is set to OFF.

Accordingly, the semiconductor bodies 20 of the unselected third stringunit SU2 and the semiconductor bodies 20 of the unselected fourth stringunit SU3 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the firststring unit SU0, the potentials of the semiconductor bodies 20 of theselected first string unit SU0 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedsecond string unit SU1 which is in the same sub-block 200 a as the firststring unit SU0 are not connected to the source layer SL; and thevoltage stress (the read disturbance) in the read operation applied tothe memory cells of the second string unit SU1 can be suppressed.

When the second string unit SU1 is selected, the bottom selecttransistor STSB is set to ON. Further, the “H” level is applied to thefirst source-side select gate SGS0A; the first source-side selecttransistor STS0A of the second string unit SU1 is set to ON; the “L”level is applied to the second source-side select gate SGS1A; and thesecond source-side select transistor STS0A of the second string unit SU1also is set to ON.

The semiconductor bodies 20 of the selected second string unit SU1 areelectrically connected to the source layer SL.

The second source-side select transistor STS1A of the first string unitSU0 that shares the second source-side select gate SGS1A with the secondstring unit SU1 is set to OFF by the “L” level applied to the secondsource-side select gate SGS1A. Accordingly, the semiconductor bodies 20of the unselected first string unit SU0 are not electrically connectedto the source layer SL.

In the other sub-block 200 b, the “L” level is applied to the firstsource-side select gate SGS0B and the second source-side select gateSGS1B; the second source-side select transistor STS0B of the thirdstring unit SU2 is set to OFF; and the first source-side selecttransistor STS0B of the fourth string unit SU3 is set to OFF.

Accordingly, the semiconductor bodies 20 of the unselected third stringunit SU2 and the semiconductor bodies 20 of the unselected fourth stringunit SU3 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the secondstring unit SU1, the potentials of the semiconductor bodies 20 of theselected second string unit SU1 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedfirst string unit SU0 which is in the same sub-block 200 a as the secondstring unit SU1 are not connected to the source layer SL; and thevoltage stress (the read disturbance) in the read operation applied tothe memory cells of the first string unit SU0 can be suppressed.

When the third string unit SU2 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the firstsource-side select gate SGS0B; the first source-side select transistorSTS0B of the third string unit SU2 is set to ON; the “H” level isapplied to the second source-side select gate SGS1B; and the secondsource-side select transistor STS1B of the third string unit SU2 also isset to ON.

The semiconductor bodies 20 of the selected third string unit SU2 areelectrically connected to the source layer SL.

The first source-side select transistor STS0B of the fourth string unitSU3 that shares the first source-side select gate SGS0B with the thirdstring unit SU2 is set to OFF by the “L” level applied to the firstsource-side select gate SGS0B. Accordingly, the semiconductor bodies 20of the unselected fourth string unit SU3 are not electrically connectedto the source layer SL.

In the other sub-block 200 a, the “L” level is applied to the firstsource-side select gate SGS0A and the second source-side select gateSGS1A; the second source-side select transistor STS0A of the firststring unit SU0 is set to OFF; and the first source-side selecttransistor STS0A of the second string unit SU1 is set to OFF.

Accordingly, the semiconductor bodies 20 of the unselected first stringunit SU0 and the semiconductor bodies 20 of the unselected second stringunit SU1 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the thirdstring unit SU2, the potentials of the semiconductor bodies 20 of theselected third string unit SU2 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedfourth string unit SU3 which is in the same sub-block 200 b as the thirdstring unit SU2 are not connected to the source layer SL; and thevoltage stress (the read disturbance) in the read operation applied tothe memory cells of the fourth string unit SU3 can be suppressed.

When the fourth string unit SU3 is selected, the bottom selecttransistor STSB is set to ON. Further, the “H” level is applied to thefirst source-side select gate SGS0B; the first source-side selecttransistor STS0B of the fourth string unit SU3 is set to ON; the “L”level is applied to the second source-side select gate SGS0B; and thesecond source-side select transistor STS1B of the fourth string unit SU3also is set to ON.

The semiconductor bodies 20 of the selected fourth string unit SU3 areelectrically connected to the source layer SL.

The second source-side select transistor STS1B of the third string unitSU2 that shares the second source-side select gate SGS1B with the fourthstring unit SU3 is set to OFF by the “L” level applied to the secondsource-side select gate SGS1B. Accordingly, the semiconductor bodies 20of the unselected third string unit SU2 are not electrically connectedto the source layer SL.

In the other sub-block 200 a, the “L” level is applied to the firstsource-side select gate SGS0A and the second source-side select gateSGS1A; the second source-side select transistor STS0A of the firststring unit SU0 is set to OFF; and the first source-side selecttransistor STS0A of the second string unit SU1 is set to OFF.

Accordingly, the semiconductor bodies 20 of the unselected first stringunit SU0 and the semiconductor bodies 20 of the unselected second stringunit SU1 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the fourthstring unit SU3, the potentials of the semiconductor bodies 20 of theselected fourth string unit SU3 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedthird string unit SU2 which is in the same sub-block 200 b as the fourthstring unit SU3 are not connected to the source layer SL; and thevoltage stress (the read disturbance) in the read operation applied tothe memory cells of the third string unit SU2 can be suppressed.

Another example of the semiconductor memory device of the secondembodiment will now be described.

FIG. 17 and FIG. 18 are circuit diagrams of the other example of thesemiconductor memory device of the second embodiment.

FIG. 19 is a schematic cross-sectional view of the other example of thesemiconductor memory device of the second embodiment.

FIG. 19 shows one block 200 subdivided by two separation portions 60(slits ST) separated from each other in the Y-direction.

In the one block 200, the first string unit SU0, the second string unitSU1, the third string unit SU2, and the fourth string unit SU3 arearranged to be separated from each other in the Y-direction.

Similarly to the embodiment described above, the multiple conductivelayers 70 are stacked on the source layer SL with the insulating layers72 interposed. The multiple conductive layers 70 include the multipleword lines WL, a drain-side select gate layer, and multiple layers ofthe source-side select gate layers.

The word line WL of each layer is provided commonly for the first tofourth string units SU0 to SU3.

One layer of the drain-side select gate layers and five layers of thesource-side select gate layers are provided in the example shown in FIG.19. The multiple layers of the word lines WL are stacked between thedrain-side select gate layer and the source-side select gate layers. Thefive layers of the source-side select gate layers are stacked betweenthe source layer SL and the word line WL of the lowermost layer.

The drain-side select gate layer is divided into the four drain-sideselect gates SGD0 to SGD3 in the Y-direction by the separation portion62 a. The first to fourth drain-side select gates SGD0 to SGD3 each arecontrolled electrically independently.

As shown in FIGS. 17 and 18, the memory string of the first string unitSU0 includes the first drain-side select transistor STD0 having thefirst drain-side select gate SGD0 as a control gate.

The memory string of the second string unit SU1 includes the seconddrain-side select transistor STD1 having the second drain-side selectgate SGD1 as a control gate.

The memory string of the third string unit SU2 includes the thirddrain-side select transistor STD2 having the third drain-side selectgate SGD2 as a control gate.

The memory string of the fourth string unit SU3 includes the fourthdrain-side select transistor STD3 having the fourth drain-side selectgate SGD3 as a control gate.

As shown in FIG. 19, the multiple layers of the source-side select gatelayers include a first source-side select gate SGS0, a secondsource-side select gate SGS1, a third source-side select gate SGS2, afourth source-side select gate SGS3, and the bottom select gate SGSB.The select gates SGS0, SGS1, SGS2, SGS3, and SGSB are provided commonlyfor the first to fourth string units SU0 to SU3.

The bottom select gate SGSB is provided on the source layer SL; thefourth source-side select gate SGS3 is provided on the bottom selectgate SGSB; the third source-side select gate SGS2 is provided on thefourth source-side select gate SGS3; the second source-side select gateSGS1 is provided on the third source-side select gate SGS2; and thefirst source-side select gate SGS0 is provided on the second source-sideselect gate SGS1.

The insulating layer 72 is provided between the bottom select gate SGSBand the source layer SL and between the select gates.

As shown in FIGS. 17 and 18, the memory string of the first string unitSU0 includes a first source-side select transistor STS0 having the firstsource-side select gate SGS0 as a control gate, a second source-sideselect transistor STS1 having the second source-side select gate SGS1 asa control gate, a third source-side select transistor STS2 having thethird source-side select gate SGS2 as a control gate, a fourthsource-side select transistor STS3 having the fourth source-side selectgate SGS3 as a control gate, and the bottom select transistor STSBhaving the bottom select gate SGSB as a control gate.

In one memory string of the first string unit SU0, the five source-sideselect transistors recited above are connected in series between thesource layer SL and the memory cells MC.

The first source-side select transistor STS0 of the first string unitSU0 is a transistor of the depletion type; and the second to fourthsource-side select transistors STS1 to STS3 of the first string unit SU0are transistors of the enhancement type.

The memory string of the second string unit SU1 includes the firstsource-side select transistor STS0 having the first source-side selectgate SGS0 as a control gate, the second source-side select transistorSTS1 having the second source-side select gate SGS1 as a control gate,the third source-side select transistor STS2 having the thirdsource-side select gate SGS2 as a control gate, the fourth source-sideselect transistor STS3 having the fourth source-side select gate SGS3 asa control gate, and the bottom select transistor STSB having the bottomselect gate SGSB as a control gate.

In one memory string of the second string unit SU1, the five source-sideselect transistors recited above are connected in series between thesource layer SL and the memory cells MC.

The second source-side select transistor STS1 of the second string unitSU1 is a transistor of the depletion type; and the first, third, andfourth source-side select transistors STS0, STS2, and STS3 of the secondstring unit SU1 are transistors of the enhancement type.

The memory string of the third string unit SU2 includes the firstsource-side select transistor STS0 having the first source-side selectgate SGS0 as a control gate, the second source-side select transistorSTS1 having the second source-side select gate SGS1 as a control gate,the third source-side select transistor STS2 having the thirdsource-side select gate SGS2 as a control gate, the fourth source-sideselect transistor STS3 having the fourth source-side select gate SGS3 asa control gate, and the bottom select transistor STSB having the bottomselect gate SGSB as a control gate.

In one memory string of the third string unit SU2, the five source-sideselect transistors recited above are connected in series between thesource layer SL and the memory cells MC.

The third source-side select transistor STS2 of the third string unitSU2 is a transistor of the depletion type; and the first, second, andfourth source-side select transistors STS0, STS1, and STS3 of the thirdstring unit SU2 are transistors of the enhancement type.

The memory string of the fourth string unit SU3 includes the firstsource-side select transistor STS0 having the first source-side selectgate SGS0 as a control gate, the second source-side select transistorSTS1 having the second source-side select gate SGS1 as a control gate,the third source-side select transistor STS2 having the thirdsource-side select gate SGS2 as a control gate, the fourth source-sideselect transistor STS3 having the fourth source-side select gate SGS3 asa control gate, and the bottom select transistor STSB having the bottomselect gate SGSB as a control gate.

In one memory string of the fourth string unit SU3, the five source-sideselect transistors recited above are connected in series between thesource layer SL and the memory cells MC.

The fourth source-side select transistor STS3 of the fourth string unitSU3 is a transistor of the depletion type; and the first to thirdsource-side select transistors STS0 to STS2 of the fourth string unitSU3 are transistors of the enhancement type.

FIG. 22B is a figure (a table) illustrating the potential controls ofthe source-side select gates of the semiconductor memory device shown inFIG. 17 to FIG. 19.

In FIG. 22B, “L” and “H” illustrate the potentials applied to thesource-side select gates; and the “L” level (the first level) is apotential that is higher than the threshold voltage of the transistor ofthe depletion type and lower than the threshold voltage of thetransistor of the enhancement type. The “L” level is, for example, 0 V.The “H” level (the second level) is a positive potential that is higherthan the threshold voltage of the transistor of the enhancement type.Accordingly, when the “L” voltage is applied to the select gate, thetransistor of the depletion type is set ON and the transistor of theenhancement type is set to OFF; and when the “H” voltage is applied tothe select gate, the transistors of the depletion type and theenhancement type each are set to ON.

Any one of the string units of the first to fourth string units SU0 toSU3 inside one block 200 is selected by the source-side selecttransistors STS0, STS1, STS2, STS3, and STSB.

When the first string unit SU0 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the firstsource-side select gate SGS0; and the first source-side selecttransistor STS0 of the first string unit SU0 is set to ON. The “H” levelis applied to the second to fourth source-side select gates SGS1 toSGS3; and the second to fourth source-side select transistors STS1 toSTS3 of the first string unit SU0 also are set to ON.

The semiconductor bodies 20 of the selected first string unit SU0 areelectrically connected to the source layer SL.

The first source-side select transistor STS0 of the enhancement type isset to OFF by the “L” level applied to the first source-side select gateSGS0 for the second to fourth string units SU1 to SU3. Accordingly, thesemiconductor bodies 20 of the unselected second to fourth string unitsSU1 to SU3 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the firststring unit SU0, the potentials of the semiconductor bodies 20 of theselected first string unit SU0 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedsecond to fourth string units SU1 to SU3 which are in the same block 200as the first string unit SU0 are not connected to the source layer SL;and the voltage stress (the read disturbance) in the read operationapplied to the memory cells of the second to fourth string units SU1 toSU3 can be suppressed.

When the second string unit SU1 is selected, the bottom selecttransistor STSB is set to ON. Further, the “L” level is applied to thesecond source-side select gate SGS1; and the second source-side selecttransistor STS1 of the second string unit SU1 is set to ON. The “H”level is applied to the first, third, and fourth source-side selectgates SGS0, SGS2, and SGS3; and the first, third, and fourth source-sideselect transistors STS0, STS2, and STS3 of the first string unit SU0also are set to ON.

The semiconductor bodies 20 of the selected second string unit SU1 areelectrically connected to the source layer SL.

The second source-side select transistor STS1 of the enhancement type isset to OFF by the “L” level applied to the second source-side selectgate SGS1 for the first, third, and fourth string units SU0, SU2, andSU3. Accordingly, the semiconductor bodies 20 of the unselected first,third, and fourth string units SU0, SU2, and SU3 are not electricallyconnected to the source layer SL.

When the read operation is executed for the memory cells of the secondstring unit SU1, the potentials of the semiconductor bodies 20 of theselected second string unit SU1 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedfirst, third, and fourth string units SU0, SU2, and SU3 which are in thesame block 200 as the second string unit SU1 are not connected to thesource layer SL; and the voltage stress (the read disturbance) in theread operation applied to the memory cells of the first, third, andfourth string units SU0, SU2, and SU3 can be suppressed.

When the third string unit SU2 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the thirdsource-side select gate SGS2; and the third source-side selecttransistor STS2 of the third string unit SU2 is set to ON. The “H” levelis applied to the first, second, and fourth source-side select gatesSGS0, SGS1, and SGS3; and the first, second, and fourth source-sideselect transistors STS0, STS1, and STS3 of the third string unit SU2also are set to ON.

The semiconductor bodies 20 of the selected third string unit SU2 areelectrically connected to the source layer SL.

The third source-side select transistor STS2 of the enhancement type isset to OFF by the “L” level applied to the third source-side select gateSGS2 for the first, second, and fourth string units SU0, SU1, and SU3.Accordingly, the semiconductor bodies 20 of the unselected first,second, and fourth string units SU0, SU1, and SU3 are not electricallyconnected to the source layer SL.

When the read operation is executed for the memory cells of the thirdstring unit SU2, the potentials of the semiconductor bodies 20 of theselected third string unit SU2 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedfirst, second, and fourth string units SU0, SU1, and SU3 which are inthe same block 200 as the third string unit SU2 are not connected to thesource layer SL; and the voltage stress (the read disturbance) in theread operation applied to the memory cells of the first, second, andfourth string units SU0, SU1, and SU3 can be suppressed.

When the fourth string unit SU3 is selected, the bottom selecttransistor STSB is set to ON. Further, the “L” level is applied to thefourth source-side select gate SGS3; and the fourth source-side selecttransistor STS3 of the fourth string unit SU3 is set to ON. The “H”level is applied to the first to third source-side select gates SGS0 toSGS2; and the first to third source-side select transistors STS0 to STS2of the fourth string unit SU3 also are set to ON.

The semiconductor bodies 20 of the selected fourth string unit SU3 areelectrically connected to the source layer SL.

The fourth source-side select transistor STS3 of the enhancement type isset to OFF by the “L” level applied to the fourth source-side selectgate SGS3 for the first to third string units SU0 to SU2. Accordingly,the semiconductor bodies 20 of the unselected first to third stringunits SU0 to SU2 are not electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the fourthstring unit SU3, the potentials of the semiconductor bodies 20 of theselected fourth string unit SU3 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedfirst to third string units SU0 to SU2 which are in the same block 200as the fourth string unit SU3 are not connected to the source layer SL;and the voltage stress (the read disturbance) in the read operationapplied to the memory cells of the first to third string units SU0 toSU2 can be suppressed.

Yet another example of the semiconductor memory device of the secondembodiment will now be described.

FIG. 20 is a circuit diagram of the other example of the semiconductormemory device of the second embodiment.

FIG. 21 is a schematic cross-sectional view of the other example of thesemiconductor memory device of the second embodiment.

FIG. 21 shows one block 200 subdivided by the two separation portions 60(the slits ST) separated from each other in the Y-direction.

In the one block 200, the first string unit SU0, the second string unitSU1, the third string unit SU2, the fourth string unit SU3, a fifthstring unit SU4, and a sixth string unit SU5 are arranged to beseparated from each other in the Y-direction.

Similarly to the embodiment described above, the multiple conductivelayers 70 are stacked on the source layer SL with the insulating layers72 interposed. The multiple conductive layers 70 include the multipleword lines WL, a drain-side select gate layer, and multiple layers ofthe source-side select gate layers.

The word line WL of each layer is provided commonly for the first tosixth string units SU0 to SU5.

One layer of the drain-side select gate layers and five layers of thesource-side select gate layers are provided in the example shown in FIG.21. The multiple layers of the word lines WL are stacked between thedrain-side select gate layer and the source-side select gate layers. Thefive layers of the source-side select gate layers are stacked betweenthe source layer SL and the word line WL of the lowermost layer.

The drain-side select gate layer is divided into the six drain-sideselect gates SGD0 to SGD5 in the Y-direction by the separation portion62 a. The first to sixth drain-side select gates SGD0 to SGD5 each arecontrolled electrically independently.

As shown in FIG. 20, the memory string of the first string unit SU0includes the first drain-side select transistor STD0 having the firstdrain-side select gate SGD0 as a control gate.

The memory string of the second string unit SU1 includes the seconddrain-side select transistor STD1 having the second drain-side selectgate SGD1 as a control gate.

The memory string of the third string unit SU2 includes the thirddrain-side select transistor STD2 having the third drain-side selectgate SGD2 as a control gate.

The memory string of the fourth string unit SU3 includes the fourthdrain-side select transistor STD3 having the fourth drain-side selectgate SGD3 as a control gate.

The memory string of the fifth string unit SU4 includes a fifthdrain-side select transistor STD4 having the fifth drain-side selectgate SGD4 as a control gate.

The memory string of the sixth string unit SU5 includes a sixthdrain-side select transistor STD5 having the sixth drain-side selectgate SGD5 as a control gate.

As shown in FIG. 21, the multiple layers of the source-side select gatelayers include the first source-side select gate SGS0, the secondsource-side select gate SGS1, the third source-side select gate SGS2,the fourth source-side select gate SGS3, and the bottom select gateSGSB. The select gates SGS0, SGS1, SGS2, SGS3, and SGSB are providedcommonly for the first to sixth string units SU0 to SU5.

The bottom select gate SGSB is provided on the source layer SL; thefourth source-side select gate SGS3 is provided on the bottom selectgate SGSB; the third source-side select gate SGS2 is provided on thefourth source-side select gate SGS3; the second source-side select gateSGS1 is provided on the third source-side select gate SGS2; and thefirst source-side select gate SGS0 is provided on the second source-sideselect gate SGS1.

The insulating layer 72 is provided between the bottom select gate SGSBand the source layer SL and between the select gates.

As shown in FIG. 20, the memory strings of the first to sixth stringunits SU0 to SU5 each include the first source-side select transistorSTS0 having the first source-side select gate SGS0 as a control gate,the second source-side select transistor STS1 having the secondsource-side select gate SGS1 as a control gate, the third source-sideselect transistor STS2 having the third source-side select gate SGS2 asa control gate, the fourth source-side select transistor STS3 having thefourth source-side select gate SGS3 as a control gate, and the bottomselect transistor STSB having the bottom select gate SGSB as a controlgate.

In one memory string of each string unit, the five source-side selecttransistors recited above are connected in series between the sourcelayer SL and the memory cells MC.

The first source-side select transistor STS0 and the second source-sideselect transistor STS1 of the first string unit SU0 are transistors ofthe depletion type; and the third source-side select transistor STS2 andthe fourth source-side select transistor STS3 of the first string unitSU0 are transistors of the enhancement type.

The first source-side select transistor STS0 and the third source-sideselect transistor STS2 of the second string unit SU1 are transistors ofthe depletion type; and the second source-side select transistor STS1and the fourth source-side select transistor STS3 of the second stringunit SU1 are transistors of the enhancement type.

The first source-side select transistor STS0 and the fourth source-sideselect transistor STS3 of the third string unit SU2 are transistors ofthe depletion type; and the second source-side select transistor STS1and the third source-side select transistor STS2 of the third stringunit SU2 are transistors of the enhancement type.

The second source-side select transistor STS1 and the third source-sideselect transistor STS2 of the fourth string unit SU3 are transistors ofthe depletion type; and the first source-side select transistor STS0 andthe fourth source-side select transistor STS3 of the fourth string unitSU3 are transistors of the enhancement type.

The second source-side select transistor STS1 and the fourth source-sideselect transistor STS3 of the fifth string unit SU4 are transistors ofthe depletion type; and the first source-side select transistor STS0 andthe third source-side select transistor STS2 of the fifth string unitSU4 are transistors of the enhancement type.

The third source-side select transistor STS2 and the fourth source-sideselect transistor STS3 of the sixth string unit SU5 are transistors ofthe depletion type; and the first source-side select transistor STS0 andthe second source-side select transistor STS1 of the sixth string unitSU5 are transistors of the enhancement type.

FIG. 22C is a figure (a table) illustrating the potential controls ofthe source-side select gates of the semiconductor memory device shown inFIGS. 20 and 21.

In FIG. 22C, “L” and “H” illustrate the potentials applied to thesource-side select gates; and the “L” level (the first level) is apotential that is higher than the threshold voltage of the transistor ofthe depletion type and lower than the threshold voltage of thetransistor of the enhancement type. The “L” level is, for example, 0 V.The “H” level (the second level) is a positive potential that is higherthan the threshold voltage of the transistor of the enhancement type.

Any one of the string units of the first to sixth string units SU0 toSU5 inside one block 200 is selected by the source-side selecttransistors STS0, STS1, STS2, STS3, and STSB.

When the first string unit SU0 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the firstsource-side select gate SGS0 and the second source-side select gateSGS1; and the first source-side select transistor STS0 and the secondsource-side select transistor STS1 of the first string unit SU0 are setto ON. Further, the “H” level is applied to the third source-side selectgate SGS2 and the fourth source-side select gate SGS3; and the thirdsource-side select transistor STS2 and the fourth source-side selecttransistor STS3 of the first string unit SU0 also are set to ON.

The semiconductor bodies 20 of the selected first string unit SU0 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the first source-side select gate SGS0 andthe second source-side select gate SGS1 for the second to sixth stringunits SU1 to SU5. Accordingly, the semiconductor bodies 20 of theunselected second to sixth string units SU1 to SU5 are not electricallyconnected to the source layer SL.

When the read operation is executed for the memory cells of the firststring unit SU0, the potentials of the semiconductor bodies 20 of theselected first string unit SU0 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedsecond to sixth string units SU1 to SU5 which are in the same block 200as the first string unit SU0 are not connected to the source layer SL;and the voltage stress (the read disturbance) in the read operationapplied to the memory cells of the second to sixth string units SU1 toSU5 can be suppressed.

When the second string unit SU1 is selected, the bottom selecttransistor STSB is set to ON. Further, the “L” level is applied to thefirst source-side select gate SGS0 and the third source-side select gateSGS2; and the first source-side select transistor STS0 and the thirdsource-side select transistor STS2 of the second string unit SU1 are setto ON. Further, the “H” level is applied to the second source-sideselect gate SGS1 and the fourth source-side select gate SGS3; and thesecond source-side select transistor STS1 and the fourth source-sideselect transistor STS3 of the second string unit SU1 also are set to ON.

The semiconductor bodies 20 of the selected second string unit SU1 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the first source-side select gate SGS0 andthe third source-side select gate SGS2 for the string units other thanthe second string unit SU1. Accordingly, the semiconductor bodies 20 ofthe unselected string units other than the second string unit SU1 arenot electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the secondstring unit SU1, the potentials of the semiconductor bodies 20 of theselected second string unit SU1 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedstring units that are in the same block 200 as the second string unitSU1 are not connected to the source layer SL; and the voltage stress(the read disturbance) in the read operation applied to the memory cellsof the unselected string units can be suppressed.

When the third string unit SU2 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the firstsource-side select gate SGS0 and the fourth source-side select gateSGS3; and the first source-side select transistor STS0 and the fourthsource-side select transistor STS3 of the third string unit SU2 are setto ON. Further, the “H” level is applied to the second source-sideselect gate SGS1 and the third source-side select gate SGS2; and thesecond source-side select transistor STS1 and the third source-sideselect transistor STS2 of the third string unit SU2 also are set to ON.

The semiconductor bodies 20 of the selected third string unit SU2 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the first source-side select gate SGS0 andthe fourth source-side select gate SGS3 for the string units other thanthe third string unit SU2. Accordingly, the semiconductor bodies 20 ofthe unselected string units other than the third string unit SU2 are notelectrically connected to the source layer SL.

When the read operation is executed for the memory cells of the thirdstring unit SU2, the potentials of the semiconductor bodies 20 of theselected third string unit SU2 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedstring units that are in the same block 200 as the third string unit SU2are not connected to the source layer SL; and the voltage stress (theread disturbance) in the read operation applied to the memory cells ofthe unselected string units can be suppressed.

When the fourth string unit SU3 is selected, the bottom selecttransistor STSB is set to ON. Further, the “L” level is applied to thesecond source-side select gate SGS1 and the third source-side selectgate SGS2; and the second source-side select transistor STS1 and thethird source-side select transistor STS2 of the fourth string unit SU3are set to ON. Further, the “H” level is applied to the firstsource-side select gate SGS0 and the fourth source-side select gateSGS3; and the first source-side select transistor STS0 and the fourthsource-side select transistor STS3 of the fourth string unit SU3 alsoare set to ON.

The semiconductor bodies 20 of the selected fourth string unit SU3 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the second source-side select gate SGS1 andthe third source-side select gate SGS2 for the string units other thanthe fourth string unit SU3. Accordingly, the semiconductor bodies 20 ofthe unselected string units other than the fourth string unit SU3 arenot electrically connected to the source layer SL.

When the read operation is executed for the memory cells of the fourthstring unit SU3, the potentials of the semiconductor bodies 20 of theselected fourth string unit SU3 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedstring units that are in the same block 200 as the fourth string unitSU3 are not connected to the source layer SL; and the voltage stress(the read disturbance) in the read operation applied to the memory cellsof the unselected string units can be suppressed.

When the fifth string unit SU4 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the secondsource-side select gate SGS1 and the fourth source-side select gateSGS3; and the second source-side select transistor STS1 and the fourthsource-side select transistor STS3 of the fifth string unit SU4 are setto ON. Further, the “H” level is applied to the first source-side selectgate SGS0 and the third source-side select gate SGS2; and the firstsource-side select transistor STS0 and the third source-side selecttransistor STS2 of the fifth string unit SU4 also are set to ON.

The semiconductor bodies 20 of the selected fifth string unit SU4 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the second source-side select gate SGS1 andthe fourth source-side select gate SGS3 for the string units other thanthe fifth string unit SU4. Accordingly, the semiconductor bodies 20 ofthe unselected string units other than the fifth string unit SU4 are notelectrically connected to the source layer SL.

When the read operation is executed for the memory cells of the fifthstring unit SU4, the potentials of the semiconductor bodies 20 of theselected fifth string unit SU4 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedstring units that are in the same block 200 as the fifth string unit SU4are not connected to the source layer SL; and the voltage stress (theread disturbance) in the read operation applied to the memory cells ofthe unselected string units can be suppressed.

When the sixth string unit SU5 is selected, the bottom select transistorSTSB is set to ON. Further, the “L” level is applied to the thirdsource-side select gate SGS2 and the fourth source-side select gateSGS3; and the third source-side select transistor STS2 and the fourthsource-side select transistor STS3 of the sixth string unit SU5 are setto ON. Further, the “H” level is applied to the first source-side selectgate SGS0 and the second source-side select gate SGS1; and the firstsource-side select transistor STS0 and the second source-side selecttransistor STS1 of the sixth string unit SU5 also are set to ON.

The semiconductor bodies 20 of the selected sixth string unit SU5 areelectrically connected to the source layer SL.

The source-side select transistor of the enhancement type is set to OFFby the “L” level applied to the third source-side select gate SGS2 andthe fourth source-side select gate SGS3 for the string units other thanthe sixth string unit SU5. Accordingly, the semiconductor bodies 20 ofthe unselected string units other than the sixth string unit SU5 are notelectrically connected to the source layer SL.

When the read operation is executed for the memory cells of the sixthstring unit SU5, the potentials of the semiconductor bodies 20 of theselected sixth string unit SU5 are set to the potential of the sourcelayer SL. At this time, the semiconductor bodies 20 of the unselectedstring units that are in the same block 200 as the sixth string unit SU5are not connected to the source layer SL; and the voltage stress (theread disturbance) in the read operation applied to the memory cells ofthe unselected string units can be suppressed.

The source-side select transistor has a structure similar to that of thememory cell. In other words, the source-side select transistor includesthe semiconductor body 20, the source-side select gate, and the memoryfilm 30 including the charge storage film 32 provided between thesemiconductor body 20 and the source-side select gate.

After forming the memory cell array, the erase operation (the injectionof holes into the charge storage film 32) is executed collectively forall of the source-side select transistors inside the same block 200; andthe source-side select transistors are set to the depletion type.

Subsequently, the program operation (the storing of electrons in thecharge storage film 32) is executed for the source-side selecttransistors to be set to the enhancement type; and the programmedsource-side select transistors are set to the enhancement type. At thistime, the selection of the string unit is performed by the drain-sideselect gates.

In the second embodiment, the number of string units disposed inside oneblock 200 subdivided by the separation portions 60 (the slits ST) may be7 or more. The number of string units and the number of layers ofsource-side select gates (other than the bottom gate) can be specifiedas follows.

Namely, the semiconductor memory device of the second embodimentincludes k layers of source-side select gates (k being a natural numberof 3 or more) and the first to nth string units (n being a naturalnumber of 3 or more) that each include multiple memory strings. Thememory strings each include a select transistor of the depletion typeand a select transistor of the enhancement type connected in series toeach other.

Among the first to nth string units, one string unit is selected and theother string units are unselected by setting the source-side selectgates connected to the source-side select transistors of the depletiontype included in the one string unit to the first level and by settingthe source-side select gates connected to the source-side selecttransistors of the enhancement type to the second level.

Among the k layers of the source-side select gates, one string unit isselected and the other string units are unselected by setting the hlayers of the select gates to the first level and by setting the (k−h)layers of the select gates to the second level. n is a number of notmore than k!/((k−h)!×h!).

The structure and the method for controlling the drain-side selecttransistor of the first embodiment are applicable to the drain-sideselect transistor of the second embodiment.

In the second embodiment, the two ends in the Y-direction of thedrain-side select gate contact the separation portion 62 a and do notcontact the separation portions 60 (the slits ST) for each of thedrain-side select gates SGD1 and SGD2 shown in FIG. 19 and thedrain-side select gates SGD1, SGD2, SGD3, and SGD4 shown in FIG. 21.

The select gates and the word lines WL are formed by, for example,filling tungsten into the gap between the insulating layers 72 from theslit ST side and by subsequently dividing the drain-side select gate inthe Y-direction by the separation portion 62 a.

A wide width of the portion between the slit ST and the columnarportions CL of the drain-side select gate adjacent to the slit ST iseasily ensured. On the other hand, the width of the portion of thedrain-side select gate not adjacent to the slit ST between theseparation portion 62 a and the columnar portions CL easily can benarrower than the width of the portion between the slit ST and thecolumnar portions CL of the drain-side select gate adjacent to the slitST. Accordingly, the resistance of the drain-side select gate notadjacent to the slit ST easily can be higher than the resistance of thedrain-side select gate adjacent to the slit ST. This may increase thetime constant of the drain-side select gate not adjacent to the slit STand delay the access time.

FIG. 24 and FIG. 25 are circuit diagrams of a semiconductor memorydevice of a third embodiment.

FIG. 26 is a schematic cross-sectional view of the semiconductor memorydevice of the third embodiment.

FIG. 34A is a table illustrating the potential controls of thedrain-side select gates SGD0 to SGD3 and the source-side select gatesSGS0 to SGS3 of the semiconductor memory device shown in FIGS. 24 to 26.

Similarly to the embodiments described above, the D-type shown in FIG.24 and FIG. 25 illustrates the transistor of the depletion type; and theE-type illustrates the transistor of the enhancement type. The D-typeand the E-type in FIG. 27 and subsequent figures are defined similarly.

The “L” level and the “H” level shown in FIG. 34A are defined similarlyto the embodiments described above. The “L” level and the “H” level ofFIGS. 34B to 34D also are defined similarly.

In the third embodiment, multiple layers of the drain-side select gatesSGD0 to SGD3 are provided also on the drain side similarly to the sourceside. The drain-side select gate layer that is provided in the uppermostlayer is divided into the four drain-side select gates SGDT0, SGDT1,SGDT2, and SGDT3 by the separation portion 62 a.

The string unit SU0 includes the drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,the drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, the drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and the drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU1 includes the drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, the drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, the drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and the drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU2 includes the drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, the drain-side select transistor of the enhancement type havingthe drain-side select gate SGD1 as a control gate, the drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and the drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU3 includes the drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, the drain-side select transistor of the enhancement type havingthe drain-side select gate SGD1 as a control gate, the drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and the drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string units SU0 to SU3 each are selected by the “L” level or the“H” level being applied to the select gates as shown in FIG. 34A.

Similarly to the embodiments described above, for example, thethresholds of the select transistors are preset to the enhancement typeor the depletion type by performing the erase operation and/or theprogram operation for the select transistors when testing in die sortingor the like before shipping. The selection of the string units SU0 toSU3 when programming is performed by the drain-side select gates SGDT0,SGDT1, SGDT2, and SGDT3 divided by the separation portion 62 a.

When used by a user, one string unit is selected by applying, to thedrain-side select gates SGDT0, SGDT1, SGDT2, and SGDT3, prescribedvoltages that set the drain-side select transistors having thedrain-side select gates SGDT0, SGDT1, SGDT2, and SGDT3 as control gatesto ON, and by applying prescribed voltages to the drain-side selectgates SGD0 to SGD3.

Because the drain-side select gates SGDT1 and SGDT2 are not adjacent tothe slit ST, the time constant may increase and the access time may bedelayed. However, because the select operations that use the drain-sideselect gates SGDT1 and SGDT2 are only when programming when die sortingto set the transistors having the drain-side select gates SGD0 to SGD3as control gates to the enhancement type, the access time is not aproblem.

Normally, when used by the user, the drain-side select gates SGDT0,SGDT1, SGDT2, and SGDT3 are constantly ON; and one string unit isselected by the drain-side select gates SGD0 to SGD3; therefore,high-speed access is possible.

FIG. 27 is a circuit diagram of another example of the semiconductormemory device of the third embodiment.

FIG. 28 is a schematic cross-sectional view of the other example of thesemiconductor memory device of the third embodiment.

FIG. 34B is a table illustrating the potential controls of thedrain-side select gates SGD0 to SGD3 and the source-side select gatesSGS0 to SGS3 of the semiconductor memory device shown in FIG. 27 andFIG. 28.

In the example as well, multiple layers of the drain-side select gatesSGD0 to SGD3 are provided on the drain side. The drain-side select gatelayer that is provided in the uppermost layer is divided into the sixdrain-side select gates SGDT0, SGDT1, SGDT2, SGDT3, SGDT4, and SGDT5 bythe separation portion 62 a. Also, a dummy gate SGDD may be providedbetween the drain-side select gate SGD0 and the drain-side select gatesSGDT0 to SGDT5.

The string unit SU0 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU1 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the enhancementtype having the drain-side select gate SGD3 as a control gate.

The string unit SU2 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string unit SU3 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the enhancementtype having the drain-side select gate SGD3 as a control gate.

The string unit SU4 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string unit SU5 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the depletiontype having the drain-side select gate SGD3 as a control gate.

As shown in FIG. 34B, the string units SU0 to SU5 each are selected bythe “L” level or the “H” level being applied to the drain-side selectgates SGD0 to SGD3. The levels shown in FIG. 34A are applied to thesource-side select gates SGS0 to SGS3. When the “L” voltage is appliedto the select gate, the transistor of the depletion type is set to ONand the transistor of the enhancement type is set to OFF; and when the“H” voltage is applied to the select gate, the transistors of thedepletion type and the enhancement type each are set to ON; thereby, onestring unit is selected.

Similarly to the embodiments described above, for example, thethresholds of the select transistors are preset to the enhancement typeor the depletion type by the erase operation and/or the programoperation for the select transistors when testing in the die sorting orthe like before shipping. The selection of the string units SU0 to SU5when programming is performed by the drain-side select gates SGDT0 toSGDT5 divided by the separation portion 62 a.

When used by the user, one string unit is selected by applying, to thedrain-side select gates SGDT0 to SGDT5, prescribed voltages that set thedrain-side select transistors having the drain-side select gates SGDT0to SGDT5 as control gates to ON, and by applying prescribed voltages tothe drain-side select gates SGD0 to SGD3.

Because the drain-side select gates SGDT1 to SGDT4 are not adjacent tothe slit ST, the time constant may increase and the access time may bedelayed. However, because the select operations that use the drain-sideselect gates SGDT1 to SGDT4 are only when programming when die sortingto set the transistors having the drain-side select gates SGD0 to SGD3as control gates to the enhancement type, the access time is not aproblem.

Normally, when used by the user, the drain-side select gates SGDT0 toSGDT5 are constantly ON; and one string unit is selected by thedrain-side select gates SGD0 to SGD3; therefore, high-speed access ispossible.

FIG. 29 and FIG. 30 are circuit diagrams of a semiconductor memorydevice of a fourth embodiment.

FIG. 31 is a schematic cross-sectional view of the semiconductor memorydevice of the fourth embodiment.

FIG. 34C is a table illustrating potential controls of the drain-sideselect gates SGD0 to SGD3 of the semiconductor memory device shown inFIG. 29 to FIG. 31.

Other than using one layer of the source-side select gates SGS on thesource side, the fourth embodiment is the same as the third embodimentrecited above.

The string unit SU0 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU1 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU2 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the enhancementtype having the drain-side select gate SGD3 as a control gate.

The string unit SU3 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string units SU0 to SU3 each are selected by the “L” level or the“H” level being applied to the select gates as shown in FIG. 34C.

Similarly to the embodiments described above, for example, thethresholds of the select transistors are preset to the enhancement typeor the depletion type by the erase operation and/or the programoperation for the select transistors when testing in the die sorting orthe like before shipping.

The selection of the string units SU0 to SU3 when programming isperformed by the drain-side select gates SGDT0, SGDT1, SGDT2, and SGDT3divided by the separation portion 62 a.

When used by the user, one string unit is selected by applying, to thedrain-side select gates SGDT0, SGDT1, SGDT2, and SGDT3, prescribedvoltages that set the drain-side select transistors having thedrain-side select gates SGDT0, SGDT1, SGDT2, and SGDT3 as control gatesto ON, and by applying prescribed voltages to the drain-side selectgates SGD0 to SGD3.

Because the drain-side select gates SGDT1 and SGDT2 are not adjacent tothe slit ST, the time constant may increase and the access time may bedelayed. However, because the select operations that use the drain-sideselect gates SGDT1 and SGDT2 are only when programming when die sortingto set the transistors having the drain-side select gates SGD0 to SGD3as control gates to the enhancement type, the access time is not aproblem.

Normally, when used by the user, the drain-side select gates SGDT0,SGDT1, SGDT2, and SGDT3 are constantly ON; and one string unit isselected by the drain-side select gates SGD0 to SGD3; therefore,high-speed access is possible.

FIG. 32 is a circuit diagram of another example of the semiconductormemory device of the fourth embodiment.

FIG. 33 is a schematic cross-sectional view of the other example of thesemiconductor memory device of the fourth embodiment.

FIG. 34D is a table illustrating the potential controls of thedrain-side select gates SGD0 to SGD3 of the semiconductor memory deviceshown in FIG. 32 and FIG. 33.

The string unit SU0 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of theenhancement type having the drain-side select gate SGD3 as a controlgate.

The string unit SU1 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the enhancementtype having the drain-side select gate SGD3 as a control gate.

The string unit SU2 includes a drain-side select transistor of thedepletion type having the drain-side select gate SGD0 as a control gate,a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string unit SU3 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the enhancementtype having the drain-side select gate SGD3 as a control gate.

The string unit SU4 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the depletion type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the enhancement type having the drain-side select gateSGD2 as a control gate, and a drain-side select transistor of thedepletion type having the drain-side select gate SGD3 as a control gate.

The string unit SU5 includes a drain-side select transistor of theenhancement type having the drain-side select gate SGD0 as a controlgate, a drain-side select transistor of the enhancement type having thedrain-side select gate SGD1 as a control gate, a drain-side selecttransistor of the depletion type having the drain-side select gate SGD2as a control gate, and a drain-side select transistor of the depletiontype having the drain-side select gate SGD3 as a control gate.

The “L” level or the “H” level is applied to the drain-side select gatesSGD0 to SGD3 as shown in FIG. 34D for the string units SU0 to SU5. Whenthe “L” voltage is applied to the select gate, the transistor of thedepletion type is set to ON and the transistor of the enhancement typeis set to OFF; and when the “H” voltage is applied to the select gate,the transistors of the depletion type and the enhancement type each areset to ON; thereby, one string unit is selected.

Similarly to the embodiments described above, for example, thethresholds of the select transistors are preset to the enhancement typeor the depletion type by the erase operation and/or the programoperation for the select transistors when testing in the die sorting orthe like before shipping. The selection of the string units SU0 to SU5when programming is performed by the drain-side select gates SGDT0 toSGDT5 divided by the separation portion 62 a.

When used by the user, one string unit is selected by applying, to thedrain-side select gates SGDT0 to SGDT5, prescribed voltages that set thedrain-side select transistors having the drain-side select gates SGDT0to SGDT5 as control gates ON and by applying prescribed voltages to thedrain-side select gates SGD0 to SGD3.

Because the drain-side select gates SGDT1 to SGDT4 are not adjacent tothe slit ST, the time constant may increase and the access time may bedelayed. However, because the select operations that use the drain-sideselect gates SGDT1 to SGDT4 are only when programming when die sortingto set the transistors having the drain-side select gates SGD0 to SGD3as control gates to the enhancement type, the access time is not aproblem.

Normally, when used by the user, the drain-side select gates SGDT0 toSGDT5 are constantly ON; and one string unit is selected by thedrain-side select gates SGD0 to SGD3; therefore, high-speed access ispossible.

In the third and fourth embodiments, it is also possible to easily setthe drain-side select transistors having the drain-side select gatesSGDT0 to SGDT5 as control gates to be constantly ON when used by theuser by setting the thresholds to be low by performing the eraseoperation after the programming that sets the drain-side selecttransistors to the enhancement type in the die sort test.

Normally, when used by the user, for example, it is also possible toapply an internal power supply voltage to the drain-side select gatesSGDT0 to SGDT5 because the drain-side select transistors having thedrain-side select gates SGDT0 to SGDT5 as control gates are constantlyset to ON.

The dummy gate SGDD may be provided between the drain-side select gateSGD0 and the drain-side select gates SGDT0 to SGDT5. A dummy gate may beprovided between the drain-side select gate SGD3 and the word lines WL.A dummy gate may be provided between the source-side select gate SGS0and the word lines WL. The dummy gate SGDD may be provided between thesource-side select gate SGSB and the source-side select gate SGS3.

A fifth embodiment will now be described.

FIG. 35A is a drawing illustrating the threshold of the memory cell andthe allotment of the data in the case where one bit of data is stored inone memory cell.

FIG. 35B is the waveform diagram of the word line when reading.

The threshold of the memory cell is set to “Z” by the erase operationand “A” by the program operation.

When reading, the cell is set to ON when the voltage “AR” is applied tothe word line linked to the gate of the memory cell and when thethreshold of the memory cell is “Z;” therefore, the level of the bitline linked to the memory cell is set to the “L” level and is read asthe “1” datum.

On the other hand, the cell is set to OFF when the threshold of thememory cell is “A;” therefore, the level of the bit line linked to thememory cell is set to the “H” level and is read as the “0” datum.

FIG. 36A is a drawing illustrating the threshold of the memory cell andthe allotment of the data in the case where two bits of data are storedin one memory cell.

FIGS. 36B and 36C are waveform diagrams of the word line when reading inthe case where the two bits are stored in the one memory cell.

By the erase operation, the threshold of the memory cell is set to “Z.”When programming, the memory cell is programmed to the thresholds of“A,” “B,” and “C” using the two bits of data of the Lower Page and theUpper Page.

When reading the Upper Page, the cell is set to ON when the voltage “BR”is applied to the word line linked to the gate of the memory cell andwhen the threshold of the memory cell is “Z” or “A;” therefore, thelevel of the bit line linked to the memory cell is set to the “L” leveland is read as the “1” datum.

On the other hand, the cell is set to OFF when the threshold of thememory cell is “B” or “C;” therefore, the level of the bit line linkedto the memory cell is set to the “H” level and is read as the “0” datum.

Therefore, the Upper Page can be read by one read operation.

However, when reading the Lower Page, it is necessary to perform theread operation twice by applying the voltages “AR” and “CR” to the wordline linked to the gate of the memory cell. Then, when the threshold ofthe memory cell is “Z” or “C,” the level is read as the “1” datum; andwhen the threshold of the memory cell is “A” or “B,” the level is readas the “0” datum.

Accordingly, multiple levels must be read when reading multi-bit memorythat stores multiple bits in one memory cell; and there may be a riskthat the read time is undesirably long.

According to a fifth embodiment described below, by storing one datum bysharing in multiple memory cells, it is possible to reduce the number ofreads even in the case where multiple bits are stored in the memorycells.

FIG. 37 to FIG. 39B illustrate an example in which three values (firstto third states) are set in one memory cell; and three bits are storedin two cells.

The read operation can be performed once; and the number of reads is thesame as the case where one bit of data is stored in one memory cell asshown in FIGS. 35A and 35B.

FIG. 37 is a schematic view showing the chip configuration of thesemiconductor memory device of the fifth embodiment.

The chip (the semiconductor memory device) includes multiple memory cellarrays. In the example shown in FIG. 37, the chip includes a firstmemory cell array 1 a and a second memory cell array 1 b. For example,the first memory cell array 1 a and the second memory cell array 1 b canbe configured similarly to the memory cell array 1 described above shownin FIG. 2.

The first memory cell array 1 a and the second memory cell array 1 beach include the multiple memory cells MC. The channels (thesemiconductor bodies) of the memory cells MC are connected to the bitlines BL; and the gates of the memory cells MC are connected to the wordlines WL. It is possible to simultaneously apply a voltage to the wordline WL of the cell array so that the voltages are different between thememory cell arrays 1 a and 1 b.

For example, 1 kB to 16 kB of memory cells MC are linked to one wordline WL; and the reading of these memory cells MC is performedsimultaneously. The data that is read is retained in multiple S/A DataLatches; and the data of the S/A Data Latches is output outside the chipvia a logic circuit (an arithmetic circuit) 91 and an input/outputcircuit 92.

FIG. 38A is a drawing showing the relationship of the thresholds of thememory cell of the fifth embodiment.

The threshold of the memory cell is set to “Z” by the erase operation.

FIGS. 38B and 38C are drawings showing the voltage of the word linelinked to the gate of the memory cell when reading in the fifthembodiment.

When reading the Lower Page, the read level (the read voltage) of thefirst memory cell array is “AR” and the read level of the second memorycell array is “AR;” when reading the Middle Page, the read level of thefirst memory cell array is “AR” and the read level of the second memorycell array is “BR;” when reading the Upper Page, the read level of thefirst memory cell array is “BR” and the read level of the second memorycell array is “AR;” and the datum (“L” or “H”) of one word line readfrom the memory cell array is retained in the S/A Data Latches.

FIG. 39A is a figure showing the relationship between the memory cellsand the data that is read in the fifth embodiment.

FIG. 39B is a figure showing the definition of the data that is read.

In the Lower Page, in the case where the threshold of the first memorycell is “Z” and the threshold of the second memory cell is “Z,” the readlevel of the first memory cell array is “AR;” therefore, the cell is setto ON and the bit line is set to the “L” level. The read level of thesecond memory cell array is “AR;” therefore, the cell is set to ON; andthe bit line is set to the “L” level. In the case where the data of thefirst memory cell array and the second memory cell array respectively is“L” and “L,” the read data is set to “1.”

In the Middle Page, the read level of the first memory cell array is“AR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “BR;”therefore, the cell is set to ON; and the bit line is set to the “L”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “L,” the read data isset to “1.”

In the Upper Page, the read level of the first memory cell array is“BR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “AR;”therefore, the cell is set to ON; and the bit line is set to the “L”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “L,” the read data isset to “1.”

In the Lower Page, in the case where the threshold of the first memorycell is “Z” and the threshold of the second memory cell is “A,” the readlevel of the first memory cell array is “AR;” therefore, the cell is setto ON; and the bit line is set to the “L” level. The read level of thesecond memory cell array is “AR;” therefore, the cell is set to OFF; andthe bit line is set to the “H” level. In the case where the data of thefirst memory cell array and the second memory cell array respectively is“L” and “H,” the read data is set to “1.”

In the Middle Page, the read level of the first memory cell array is“AR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “BR;”therefore, the cell is set to ON; and the bit line is set to the “L”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “L,” the read data isset to “1.”

In the Upper Page, the read level of the first memory cell array is“BR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “AR;”therefore, the cell is set to OFF; and the bit line is set to the “H”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “H,” the read data isset to “0.”

In the Lower Page, in the case where the threshold of the first memorycell is “Z” and the threshold of the second memory cell is “B,” the readlevel of the first memory cell array is “AR;” therefore, the cell is setto ON; and the bit line is set to the “L” level. The read level of thesecond memory cell array is “AR;” therefore, the cell is set to OFF; andthe bit line is set to the “H” level. In the case where the data of thefirst memory cell array and the second memory cell array respectively is“L” and “H,” the read data is set to “1.”

In the Middle Page, the read level of the first memory cell array is“AR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “BR;”therefore, the cell is set to OFF; and the bit line is set to the “H”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “H,” the read data isset to “0.”

In the Upper Page, the read level of the first memory cell array is“BR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “AR;”therefore, the cell is set to OFF; and the bit line is set to the “H”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “H,” the read data isset to “0.”

In the Lower Page, in the case where the threshold of the first memorycell is “A” and the threshold of the second memory cell is “Z,” the readlevel of the first memory cell array is “AR;” therefore, the cell is setto OFF; and the bit line is set to the “H” level. The read level of thesecond memory cell array is “AR;” therefore, the cell is set to ON; andthe bit line is set to the “L” level. In the case where the data of thefirst memory cell array and the second memory cell array respectively is“H” and “L,” the read data is set to “1.”

In the Middle Page, the read level of the first memory cell array is“AR;” therefore, the cell is set to OFF; and the bit line is set to the“H” level. The read level of the second memory cell array is “BR;”therefore, the cell is set to ON; and the bit line is set to the “L”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “H” and “L,” the read data isset to “0.”

In the Upper Page, the read level of the first memory cell array is“BR;” therefore, the cell is set to ON; and the bit line is set to the“L” level. The read level of the second memory cell array is “AR;”therefore, the cell is set to ON; and the bit line is set to the “L”level. In the case where the data of the first memory cell array and thesecond memory cell array respectively is “L” and “L,” the read data isset to “1.”

Similarly thereafter, the data that is read is determined according tothe thresholds of the first memory cell and the second memory cell asshown in FIG. 39A.

In the read operation, first, when the read operation command andaddress are input from the outside, one of the Lower Page, the MiddlePage, or the Upper Page is determined according to the address; one wordline WL of the first memory cell array 1 a and one word line WL of thesecond memory cell array 1 b shown in FIG. 37 are selected; and the wordlines WL are respectively set to the prescribed voltages shown in FIGS.38B and 38C. Then, the data of the memory cells MC linked to the wordlines WL is read via the bit lines BL; and the datum of “L” or “H” isretained respectively in the S/A Data Latches of the first memory cellarray 1 a and the second memory cell array 1 b.

Subsequently, based on an output command from the outside, one set(e.g., the data output unit of 8 bits or 16 bits) of the S/A DataLatches is selected for each of the arrays 1 a and 1 b; the datum (“L”or “H”) is input to the logic circuit (the select arithmetic circuit)91; and the “1” or “0” datum is determined according to the definitionof FIG. 39B and output outside the chip via the input/output circuit 92.

On the other hand, in the program operation, first, the data of theLower Page is input and retained in the S/A Data Latches of the firstmemory cell array 1 a and the second memory cell array 1 b via theinput/output circuit 92 and the logic circuit 91. At this time, the samedata is retained in the S/A Data Latches of the first memory cell array1 a and the second memory cell array 1 b.

Subsequently, similarly to the Lower Page, the data of the Middle Pageand the Upper Page is transmitted to the S/A Data Latches of the firstmemory cell array 1 a and the second memory cell array 1 b. At thistime, the same data is retained in the S/A Data Latches of the firstmemory cell array 1 a and the second memory cell array 1 b.

Subsequently, after the input of a program command, the data that isretained in the S/A Data Latches is converted to the data inside the S/AData Latches for Inhibit, for programming to the “A” level, and forprogramming to the “B” level for each of the first memory cell array 1 aand the second memory cell array 1 b according to the table shown inFIG. 40 and is programmed as the prescribed threshold of the memorycell.

In the case where the data input from the outside is Lower Page “1,”Middle Page “0,” and Upper Page “0,” the data to the S/A Data Latches isset as follows. Programming is performed to set the first memory cellarray to “Inhibit” (Z) and the second memory cell array to “B.” Or,programming is performed to set the first memory cell array to “B” andthe second memory cell array to “Inhibit” (Z). In the case where thenumber of cells for which the programming is not completed is countedpartway through the programming, the data is set for predeterminedhalves of the multiple S/A Data Latches so that the data can be halved.

A modification of the fifth embodiment will now be described withreference to FIG. 41A to FIG. 43.

FIGS. 41A and 41B are drawings showing the voltage of the word linelinked to the gate of the memory cell when reading in the modification.

When reading the Lower Page, the read level of the first memory cellarray is set to “AR” and the read level of the second memory cell arrayis set to “BR;” when reading the Middle Page, the read level of thefirst memory cell array is set to “BR” and the read level of the secondmemory cell array is set to “AR;” and when reading the Upper Page, theread level of the first memory cell array is set to “BR” and the readlevel of the second memory cell array is set to “BR.”

FIG. 42A is a figure illustrating the relationship between the memorycells and the data that is read in the modification.

FIG. 42B is a figure showing the definition of the data that is read.

After the input of the program command, the data that is retained in theS/A Data Latches is converted to the data of the S/A Data Latches forInhibit, for programming to the “A” level, and for programming to the“B” level for each of the first memory cell array and the second memorycell array according to the table shown in FIG. 43 and is programmed asthe prescribed threshold of the memory cell.

In the case where the data input from the outside is Lower Page “0,”Middle Page “0,” and Upper Page “0,” the data to the S/A Data Latches isset as follows. Programming is performed to set the first memory cellarray to “Inhibit” (Z) and the second memory cell array to “B.” Or,programming is performed to set the first memory cell array to “B” andthe second memory cell array to “Inhibit” (Z). In the case where thenumber of cells for which the programming is not completed is countedpartway through the programming, the data is set for predeterminedhalves of the multiple S/A Data Latches so that the data can be halved.

According to the fifth embodiment, by applying the prescribed voltagesto the word lines for each of multiple memory cell arrays, even in thecase where multiple bits are stored in one memory cell, it is possibleto set the number of reads to one read operation; and a read operationis possible in which the number of reads is the same as the case whereone bit of data is stored in one memory cell.

According to the fifth embodiment, two memory cell arrays are included;word lines are linked to the gates of the memory cells of each array;voltages that are different between the arrays are applied to the wordlines; and three bits are stored in one memory; but there may be threeor more memory cell arrays. Also, four or more bits may be stored byproviding four, five, or more thresholds of the memory cell in onememory cell.

Although according to the fifth embodiment two memory cell arrays areused as one set and three bits are stored in two cells, for example, theeight physical memory cell arrays shown in FIG. 44 may be used as oneset; and the data may be stored in the memory cells of each set.

FIG. 45 is a circuit diagram of another example of the semiconductormemory device of the first embodiment;

FIG. 46 is a schematic cross-sectional view of the semiconductor memorydevice shown in FIG. 45 of the first embodiment; and

FIG. 47A is a schematic plan view of the layer of the one block 200where the drain-side select gates SGD0, SDG1, SDG2, and SGD3 areprovided.

FIG. 47B is a schematic plan view of the layer of the one block 200where the word line WL is provided.

As shown in FIG. 46 and FIG. 47A, the separation portions 62 a dividethe one drain-side select gate layer into the first drain-side selectgate SGD0, the second drain-side select gate SGD1, the third drain-sideselect gate SGD2, and the fourth drain-side select gate SGD3.

As shown in FIG. 45, the first drain-side select gate SGD0 is connectedto the drive circuit DRV0. The second drain-side select gate SGD1 isconnected to the drive circuit DRV1. The third drain-side select gateSGD2 is connected to the drive circuit DRV2. The fourth drain-sideselect gate SGD3 is connected to the drive circuit DRV3.

The second drain-side select gate SGD1 is connected to the two drivecircuits DRV1 from both sides of the word line WL. The second drain-sideselect gate SGD1 is driven from both sides of the word line WL. Thethird drain-side select gate SGD2 is connected to the two drive circuitsDRV2 from both sides of the word line WL. The third drain-side selectgate SGD2 is driven from both sides of the word line WL.

Accordingly, even if the resistance of the drain-side select gate SGD1,SGD2 is high, the rise time of the drain-side select gate SGD1, SGD2 isnot delayed as compared with the rise time of the other drain-sideselect gate SGD0, SGD3.

The word line WL, the drain-side select gate SGD0, and the drain-sideselect gate SGD3 are driven from one side. The drain-side select gateSGD1 and the drain-side select gate SGD2 are driven from both sides ofthe word line WL.

When the first string unit SU0 is selected, the first drain-side selecttransistor having the first drain-side select gate SGD0 is set to ON.The other drain-side select transistors each having the seconddrain-side select gate SGD1, the third drain-side select gate SGD2 andthe fourth drain-side select gate SGD3 are set to OFF.

When the second string unit SU1 is selected, the second drain-sideselect transistor having the second drain-side select gate SGD1 is setto ON. The other drain-side select transistors each having the firstdrain-side select gate SGD0, the third drain-side select gate SGD2 andthe fourth drain-side select gate SGD3 are set to OFF.

When the third string unit SU2 is selected, the third drain-side selecttransistor having the third drain-side select gate SGD2 is set to ON.The other drain-side select transistors each having the first drain-sideselect gate SGD0, the second drain-side select gate SGD3 and the fourthdrain-side select gate SGD3 are set to OFF.

When the fourth string unit SU3 is selected, the fourth drain-sideselect transistor having the fourth drain-side select gate SGD3 is setto ON. The other drain-side select transistors each having the firstdrain-side select gate SGD0, the second drain-side select gate SGD3 andthe third drain-side select gate SGD2 are set to OFF.

Although the two drain-side select gates SGD0 and SGD3 are each drivenby the one drive circuit from the one side in the above embodiment, onedrain-side select gate or any plurality of drain-side select gates maybe driven by the one drive circuit from the one side.

Although the two drain-side select gates SGD1 and SGD2 are each drivenby the two drive circuits from the both sides in the above embodiment,one drain-side select gate or any plurality of drain-side select gatesmay be driven by the two drive circuits from the both sides.

In the embodiments described above, the stacked body 100 that includesthe multiple conductive layers 70 and the multiple insulating layers 72may be formed by alternately stacking the conductive layers 70 and theinsulating layers 72 without forming the sacrificial layers 71. Also, inthe embodiments described above, a dummy word line may be providedbetween the drain-side select gate and the word lines and/or between thesource-side select gate and the word lines. A prescribed voltage isapplied to the dummy word line in the read, program, and eraseoperations. Also, dummy cells may be preset to a prescribed threshold byan erase operation and a program operation.

The semiconductor memory device according to the embodiment may includethe following configuration.

Note 1

A semiconductor memory device, comprising:

first to nth string units (n being a natural number of 3 or more), thefirst to nth string units each including a memory string, the memorystring including a plurality of memory cells and a plurality of selecttransistors connected in series in a first direction;

a plurality of layers of word lines stacked in the first direction; and

(n−1) layers of select gate layers stacked in the first direction,

the (n−1) layers of select gate layers including first to (2×(n−1))thselect gates electrically isolated from each other,

the first string unit being selected by the first to (n−1)th selectgates,

the kth string unit (k being not less than 1 and not more than n) beingselected by the kth to (n+k−2)th select gates,

the nth string unit being selected by the nth to (2×(n−1))th selectgates.

Note 2

The device according to Note 1, wherein

a stacked body including the plurality of layers of word lines and the(n−1) layers of select gate layers is divided into a plurality of blocksin a second direction by a first separation portion, the firstseparation portion piercing the stacked body, and

the first to nth string units in one of the blocks are arranged to beseparated from each other in the second direction.

Note 3

The device according to Note 2, wherein

one layer of the select gate layers inside the one block is divided intotwo of the select gates by a second separation portion betweenmutually-adjacent string units of the string units,

the second separation portion divides the one layer of the select gatelayers and does not divide the other layers of the select gate layers,and

positions in the second direction of the second separation portionsprovided in different layers of the select gate layers are shifted fromeach other.

Note 4

The device according to Note 2, wherein

the memory string includes:

-   -   a semiconductor body extending through the stacked body in the        first direction; and    -   a charge storage portion provided between the semiconductor body        and one of the word lines.        Note 5

A semiconductor memory device, comprising:

a first string unit and a second string unit, the first string unit andthe second string unit each including a memory string, the memory stringincluding a plurality of memory cells and a plurality of selecttransistors connected in series in a first direction;

a plurality of layers of word lines stacked in the first direction, theplurality of layers of word lines being provided commonly for the memorycells of the first string unit and the memory cells of the second stringunit; and

a first select gate and a second select gate stacked in the firstdirection, the first select gate and the second select gate beingprovided commonly for the select transistors of the first string unitand the select transistors of the second string unit,

the first string unit including a first select transistor and a secondselect transistor, the first select transistor being of a depletion typeand being selected by the first select gate, the second selecttransistor being of an enhancement type, being selected by the secondselect gate, and being connected in series to the first selecttransistor,

the second string unit including a third select transistor and a fourthselect transistor, the third select transistor being of the enhancementtype and being selected by the first select gate, the fourth selecttransistor being of the depletion type, being selected by the secondselect gate, and being connected in series to the third selecttransistor.

Note 6

The device according to Note 5, wherein

a stacked body including the plurality of layers of word lines, thefirst select gate, and the second select gate is divided into aplurality of blocks in a second direction by a separation portion, theseparation portion piercing the stacked body, and

the first string unit and the second string unit in one of the blocksare arranged to be separated from each other in the second direction.

Note 7

The device according to Note 6, wherein

the memory string includes:

-   -   a semiconductor body extending through the stacked body in the        first direction; and    -   a charge storage portion provided between the semiconductor body        and one of the word lines, between the semiconductor body and        the first select gate, and between the semiconductor body and        the second select gate,

the first select transistor and the third select transistor are set tothe depletion type by an erase operation for the charge storage portion,and

the second select transistor and the fourth select transistor are set tothe enhancement type by a program operation for the charge storageportion.

Note 8

The device according to Note 5, wherein

the first select transistor of the depletion type and the second selecttransistor of the enhancement type are connected in series in order fromthe memory cell side between a source line and the memory cells of thefirst string unit, and

the third select transistor of the enhancement type and the fourthselect transistor of the depletion type are connected in series in orderfrom the memory cell side between the source line and the memory cellsof the second string unit.

Note 9

The device according to Note 8, wherein

when the first string unit is selected, the first select transistor, thesecond select transistor, and the fourth select transistor are set to ONand the third select transistor is set to OFF, and

when the second string unit is selected, the first select transistor,the third select transistor, and the fourth select transistor are set toON and the second select transistor is set to OFF.

Note 10

A semiconductor memory device, comprising:

first to nth string units (n being a natural number of 3 or more), thefirst to nth string units each including a memory string, the memorystring including a plurality of memory cells and a plurality of selecttransistors connected in series in a first direction;

a plurality of layers of word lines stacked in the first direction; and

k layers of select gates (k being a natural number of 3 or more) stackedin the first direction,

the memory strings each including a select transistor of a depletiontype and a select transistor of an enhancement type connected in seriesto each other,

one string unit of the first to nth string units being selected and theother string units of the first to nth string units being unselected bysetting the select gates connected to the select transistors of thedepletion type included in the one string unit to a first level and bysetting the select gates connected to the select transistors of theenhancement type included in the one string unit to a second level.

Note 11

The device according to Note 10, wherein the one string unit is selectedand the other string units are unselected by setting h layers of theselect gates of the k layers of the select gates to the first level andby setting (k−h) layers of the select gates of the k layers of theselect gates to the second level.

Note 12

The device according to Note 11, wherein n is a number not more thank!/((k−h)!×h!).

Note 13

The device according to Note 10, wherein

a stacked body including the plurality of layers of word lines and the klayers of the select gates is divided into a plurality of blocks in asecond direction by a separation portion, the separation portionpiercing the stacked body, and

the first to nth string units in one of the blocks are arranged to beseparated from each other in the second direction.

Note 14

The device according to Note 13, wherein

the memory string includes:

-   -   a semiconductor body extending through the stacked body in the        first direction; and    -   a charge storage portion provided between the semiconductor body        and one of the word lines, and between the semiconductor body        and the first to nth select gates,

the select transistors are set to the depletion type by an eraseoperation for the charge storage portion, and

the select transistors are set to the enhancement type by a programoperation for the charge storage portion.

Note 15

The device according to Note 13, wherein

the stacked body includes four layers of the select gates,

the first to fourth string units in one of the blocks are arranged to beseparated from each other in the second direction,

the first string unit includes a first select transistor of thedepletion type, a second select transistor of the enhancement type, athird select transistor of the enhancement type, and a fourth selecttransistor of the enhancement type connected in series in order from thememory cell side between a source line and the memory cells of the firststring unit,

the second string unit includes a fifth select transistor of theenhancement type, a sixth select transistor of the depletion type, aseventh select transistor of the enhancement type, and an eighth selecttransistor of the enhancement type connected in series in order from thememory cell side between the source line and the memory cells of thesecond string unit,

the third string unit includes a ninth select transistor of theenhancement type, a tenth select transistor of the enhancement type, aneleventh select transistor of the depletion type, and a twelfth selecttransistor of the enhancement type connected in series in order from thememory cell side between the source line and the memory cells of thethird string unit, and

the fourth string unit includes a thirteenth select transistor of theenhancement type, a fourteenth select transistor of the enhancementtype, a fifteenth select transistor of the enhancement type, and asixteenth select transistor of the depletion type connected in series inorder from the memory cell side between the source line and the memorycells of the fourth string unit.

Note 16

The device according to Note 15, wherein

when the first string unit is selected, the first to fourth, sixth toeighth, tenth to twelfth, and fourteenth to sixteenth select transistorsare set to ON and the other select transistors are set to OFF,

when the second string unit is selected, the first, third to ninth,eleventh to thirteenth, and fifteenth to sixteenth select transistorsare set to ON and the other select transistors are set to OFF,

when the third string unit is selected, the first to second, fourth tosixth, eighth to fourteenth, and sixteenth select transistors are set toON and the other select transistors are set to OFF, and

when the fourth string unit is selected, the first to third, fifth toseventh, ninth to eleventh, and thirteenth to sixteenth selecttransistors are set to ON and the other select transistors are set toOFF.

Note 17

The device according to Note 13, wherein

the stacked body includes four layers of the select gates,

the first to sixth string units in one of the blocks are arranged to beseparated from each other in the second direction,

the first string unit includes a first select transistor of thedepletion type, a second select transistor of the depletion type, athird select transistor of the enhancement type, and a fourth selecttransistor of the enhancement type connected in series in order from thememory cell side between a source line and the memory cells of the firststring unit,

the second string unit includes a fifth select transistor of thedepletion type, a sixth select transistor of the enhancement type, aseventh select transistor of the depletion type, and an eighth selecttransistor of the enhancement type connected in series in order from thememory cell side between the source line and the memory cells of thesecond string unit,

the third string unit includes a ninth select transistor of thedepletion type, a tenth select transistor of the enhancement type, aneleventh select transistor of the enhancement type, and a twelfth selecttransistor of the depletion type connected in series in order from thememory cell side between the source line and the memory cells of thethird string unit,

the fourth string unit includes a thirteenth select transistor of theenhancement type, a fourteenth select transistor of the depletion type,a fifteenth select transistor of the depletion type, and a sixteenthselect transistor of the enhancement type connected in series in orderfrom the memory cell side between the source line and the memory cellsof the fourth string unit,

the fifth string unit includes a seventeenth select transistor of theenhancement type, an eighteenth select transistor of the depletion type,a nineteenth select transistor of the enhancement type, and a twentiethselect transistor of the depletion type connected in series in orderfrom the memory cell side between the source line and the memory cellsof the fifth string unit, and

the sixth string unit includes a twenty-first select transistor of theenhancement type, a twenty-second select transistor of the enhancementtype, a twenty-third select transistor of the depletion type, and atwenty-fourth select transistor of the depletion type connected inseries in order from the memory cell side between the source line andthe memory cells of the sixth string unit.

Note 18

The device according to Note 17, wherein

when the first string unit is selected, the first to fifth, seventh toninth, eleventh to twelfth, fourteenth to sixteenth, eighteenth totwentieth, and twenty-third to twenty-fourth select transistors are setto ON and the other select transistors are set to OFF,

when the second string unit is selected, the first to second, fourth totenth, twelfth, fourteenth to sixteenth, eighteenth, twentieth, andtwenty-second to twenty-fourth select transistors are set to ON and theother select transistors are set to OFF,

when the third string unit is selected, the first to third, fifth toseventh, ninth to twelfth, fourteenth to fifteenth, eighteenth totwentieth, and twenty-second to twenty-fourth select transistors are setto ON and the other select transistors are set to OFF,

when the fourth string unit is selected, the first to second, fourth tofifth, seventh to ninth, twelfth to eighteenth, twentieth totwenty-first, and twenty-third to twenty-fourth select transistors areset to ON and the other select transistors are set to OFF,

when the fifth string unit is selected, the first to third, fifth,seventh, ninth, eleventh to fifteenth, seventeenth to twenty-first, andtwenty-third to twenty-fourth select transistors are set to ON and theother select transistors are set to OFF, and

when the sixth string unit is selected, the first to second, fifth toseventh, ninth to tenth, twelfth to fifteenth, seventeenth toeighteenth, and twentieth to twenty-fourth select transistors are set toON and the other select transistors are set to OFF.

Note 19

A method for manufacturing the semiconductor memory device according toNote 7,

the erase operation and the program operation being performed beforeshipping.

Note 20

A method for manufacturing the semiconductor memory device according toNote 14,

the erase operation and the program operation being performed beforeshipping.

Note 21

A semiconductor memory device, comprising first to nth memory cells (nbeing a natural number), the first to nth memory cells each having aplurality of thresholds,

the first to nth memory cells being selected simultaneously in a readoperation,

after the read operation, k pieces of read data (k being n or less)being determined from n pieces of data read from the first to nth memorycells.

Note 22

The device according to Note 21, wherein

the first to nth memory cells include a first state, a second state, athird state, and an hth state (h being 3 or more),

the first state and the second state are discriminated by applying afirst read voltage to gates of the first to nth memory cells,

the second state and the third state are discriminated by applying asecond read voltage to the gates of the first to nth memory cells,

the (h−1)th state and the hth state are discriminated by applying an(h−1)th read voltage to the gates of the first to nth memory cells, and

a voltage of the first to (h−1)th read voltages is applied to the firstto nth memory cells in the read operation.

Note 23

A semiconductor memory device, comprising a first memory cell and asecond memory cell, the first memory cell and the second memory celleach having a plurality of thresholds,

the first memory cell and the second memory cell being selectedsimultaneously in a read operation,

after the read operation, one piece of read data is determined fromfirst data read from the first memory cell and second data read from thesecond memory cell.

Note 24

The device according to Note 23, wherein

the first memory cell and the second memory cell each include a firststate, a second state, and a third state,

the first state and the second state are discriminated by applying afirst read voltage to a gate of the first memory cell and a gate of thesecond memory cell,

the second state and the third state are discriminated by applying asecond read voltage to the gate of the first memory cell and the gate ofthe second memory cell,

the read operation is performed in a first read operation by applyingthe first read voltage to the first memory cell and applying the firstread voltage to the second memory cell,

the read operation is performed in a second read operation by applyingthe first read voltage to the first memory cell and applying the secondread voltage to the second memory cell, and

the read operation is performed in a third read operation by applyingthe second read voltage to the first memory cell and applying the firstread voltage to the second memory cell.

Note 25

A semiconductor memory device, comprising:

first to nth string units (n being a natural number of 3 or more), thefirst to nth string units each including a memory string, the memorystring including a plurality of memory cells and a plurality of selecttransistors connected in series in a first direction;

a plurality of layers of word lines stacked in the first direction; and

one select gate layer stacked in the first direction,

the one select gate layer including first, second, and nth select gateselectrically isolated from each other,

the first string unit being selected by the first select gates,

the kth string unit (k being not less than 1 and not more than n) beingselected by the kth select gates,

each of h (h being not less than 1 and not more than n) select gates ofthe first, second, and nth select gates is connected to one drivecircuit,

each of i (i being not less than 1 and not more than n) select gates ofthe first, second, and nth select gates is connected to two drivecircuits.

Note 26

The device according to Note 25, wherein

the plurality of layers of word lines and the one select gate layer aredivided into a plurality of blocks in a second direction by a firstseparation portion, the first separation portion piercing a stacked bodyincluding the plurality of layers of word lines and the one select gatelayer, and

the first to nth string units in one of the blocks are arranged to beseparated from each other in the second direction.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modification as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor memory device, comprising: firstto nth string units (n being a natural number of 2 or more), the firstto nth string units each including a memory string, the memory stringincluding a drain-side select transistor, a plurality of memory cells,and a plurality of source-side select transistors, the drain-side selecttransistor, the plurality of memory cells, and the plurality ofsource-side select transistors being connected in series in a firstdirection; a plurality of drain-side select gate lines connected togates of a plurality of drain-side select transistors of a plurality ofmemory strings, the plurality of drain-side select gate lineselectrically isolated from each other; a plurality of word lines stackedin the first direction and connected to gates of the plurality of memorycells; and kth source-side select gate lines (n being a natural numberof 2 or more) stacked in the first direction and connected to gates ofthe plurality of source-side select transistors; the plurality ofsource-side select transistors including a source-side select transistorof a depletion type and a source-side select transistor of anenhancement type, the memory string including the source-side selecttransistor of the depletion type and the source-side select transistorof the enhancement type connected in series to each other, and onestring unit of the first to nth string units being selected and anotherstring units of the first to nth string units being unselected bysetting a source-side select gate connected to the source-side selecttransistor of the depletion type included in one string unit to a firstlevel and by setting a source-side select gate connected to thesource-side select transistor of the enhancement type included in theone string unit to a second level.
 2. The device according to claim 1,wherein when the source-side select transistor is preset to theenhancement type by program operation, the memory string including thesource-side select transistor to be the enhancement type is selected bythe drain-side select transistor.
 3. The device according to claim 1,wherein the memory string further includes a bottom select transistor,gates of bottom select transistors of the first to nth string units areconnected to common bottom select gate line.
 4. The device according toclaim 1, wherein when the source-side select transistor is preset to theenhancement type by program operation, the drain-side select transistorof the memory string including the source-side select transistor to bethe enhancement type is set to ON.
 5. The device according to claim 4,wherein the one string unit is selected and the other string units areunselected by setting h layers of the source-side select gates of the klayers of the source-side select gates to the first level and by setting(k−h) layers of the source-side select gates of the k layers of thesource-side select gates to the second level.
 6. The device according toclaim 5, wherein n is a number not more than k!/((k−h)!×h!).
 7. Thedevice according to claim 5, wherein a stacked body including theplurality of word lines and the k layers of the source-side select gatesis divided into a plurality of blocks in a second direction by aseparation portion, the separation portion piercing the stacked body,and the first to nth string units in one of the blocks are arranged tobe separated from each other in the second direction.
 8. The deviceaccording to claim 7, wherein the memory string includes: asemiconductor body extending through the stacked body in the firstdirection; and a charge storage portion provided between thesemiconductor body and one of the word lines, and between thesemiconductor body and the source-side select gates, the source-sideselect transistor is set to the depletion type by an erase operation forthe charge storage portion, and the select transistor is set to theenhancement type by a program operation for the charge storage portion.9. The device according to claim 5, wherein the stacked body includesfour layers of the source-side select gate lines, the first to fourthstring units in one of the blocks are arranged to be separated from eachother in the second direction, the first string unit includes a firstsource-side select transistor of the depletion type, a secondsource-side select transistor of the enhancement type, a thirdsource-side select transistor of the enhancement type, and a fourthsource-side select transistor of the enhancement type connected inseries in order from the memory cell side between a source line and thememory cells of the first string unit, the second string unit includes afifth source-side select transistor of the enhancement type, a sixthsource-side select transistor of the depletion type, a seventhsource-side select transistor of the enhancement type, and an eighthsource-side select transistor of the enhancement type connected inseries in order from the memory cell side between the source line andthe memory cells of the second string unit, the third string unitincludes a ninth source-side select transistor of the enhancement type,a tenth source-side select transistor of the enhancement type, aneleventh source-side select transistor of the depletion type, and atwelfth source-side select transistor of the enhancement type connectedin series in order from the memory cell side between the source line andthe memory cells of the third string unit, and the fourth string unitincludes a thirteenth source-side select transistor of the enhancementtype, a fourteenth source-side select transistor of the enhancementtype, a fifteenth source-side select transistor of the enhancement type,and a sixteenth source-side select transistor of the depletion typeconnected in series in order from the memory cell side between thesource line and the memory cells of the fourth string unit.
 10. Thedevice according to claim 9, wherein when the first string unit isselected, the first to fourth, sixth to eighth, tenth to twelfth, andfourteenth to sixteenth source-side select transistors are set to ON andthe other source-side select transistors are set to OFF, when the secondstring unit is selected, the first, third to ninth, eleventh tothirteenth, and fifteenth to sixteenth source-side select transistorsare set to ON and the other source-side select transistors are set toOFF, when the third string unit is selected, the first to second, fourthto sixth, eighth to fourteenth, and sixteenth source-side selecttransistors are set to ON and the other source-side select transistorsare set to OFF, and when the fourth string unit is selected, the firstto third, fifth to seventh, ninth to eleventh, and thirteenth tosixteenth source-side select transistors are set to ON and the othersource-side select transistors are set to OFF.
 11. The device accordingto claim 5, wherein the stacked body includes four layers of thesource-side select gates, the first to sixth string units in one of theblocks are arranged to be separated from each other in the seconddirection, the first string unit includes a first source-side selecttransistor of the depletion type, a second source-side select transistorof the depletion type, a third source-side select transistor of theenhancement type, and a fourth source-side select transistor of theenhancement type connected in series in order from the memory cell sidebetween a source line and the memory cells of the first string unit, thesecond string unit includes a fifth source-side select transistor of thedepletion type, a sixth source-side select transistor of the enhancementtype, a seventh source-side select transistor of the depletion type, andan eighth source-side select transistor of the enhancement typeconnected in series in order from the memory cell side between thesource line and the memory cells of the second string unit, the thirdstring unit includes a ninth source-side select transistor of thedepletion type, a tenth source-side select transistor of the enhancementtype, an eleventh source-side select transistor of the enhancement type,and a twelfth source-side select transistor of the depletion typeconnected in series in order from the memory cell side between thesource line and the memory cells of the third string unit, the fourthstring unit includes a thirteenth source-side select transistor of theenhancement type, a fourteenth source-side select transistor of thedepletion type, a fifteenth source-side select transistor of thedepletion type, and a sixteenth source-side select transistor of theenhancement type connected in series in order from the memory cell sidebetween the source line and the memory cells of the fourth string unit,the fifth string unit includes a seventeenth source-side selecttransistor of the enhancement type, an eighteenth source-side selecttransistor of the depletion type, a nineteenth source-side selecttransistor of the enhancement type, and a twentieth source-side selecttransistor of the depletion type connected in series in order from thememory cell side between the source line and the memory cells of thefifth string unit, and the sixth string unit includes a twenty-firstsource-side select transistor of the enhancement type, a twenty-secondsource-side select transistor of the enhancement type, a twenty-thirdsource-side select transistor of the depletion type, and a twenty-fourthsource-side select transistor of the depletion type connected in seriesin order from the memory cell side between the source line and thememory cells of the sixth string unit.
 12. The device according to claim11, wherein when the first string unit is selected, the first to fifth,seventh to ninth, eleventh to twelfth, fourteenth to sixteenth,eighteenth to twentieth, and twenty-third to twenty-fourth source-sideselect transistors are set to ON and the other source-side selecttransistors are set to OFF, when the second string unit is selected, thefirst to second, fourth to tenth, twelfth, fourteenth to sixteenth,eighteenth, twentieth, and twenty-second to twenty-fourth source-sideselect transistors are set to ON and the other source-side selecttransistors are set to OFF, when the third string unit is selected, thefirst to third, fifth to seventh, ninth to twelfth, fourteenth tofifteenth, eighteenth to twentieth, and twenty-second to twenty-fourthsource-side select transistors are set to ON and the other source-sideselect transistors are set to OFF, when the fourth string unit isselected, the first to second, fourth to fifth, seventh to ninth,twelfth to eighteenth, twentieth to twenty-first, and twenty-third totwenty-fourth source-side select transistors are set to ON and the othersource-side select transistors are set to OFF, when the fifth stringunit is selected, the first to third, fifth, seventh, ninth, eleventh tofifteenth, seventeenth to twenty-first, and twenty-third totwenty-fourth source-side select transistors are set to ON and the othersource-side select transistors are set to OFF, and when the sixth stringunit is selected, the first to second, fifth to seventh, ninth to tenth,twelfth to fifteenth, seventeenth to eighteenth, and twentieth totwenty-fourth source-side select transistors are set to ON and the othersource-side select transistors are set to OFF.
 13. The device accordingto claim 5, wherein the stacked body includes two layers of thesource-side select gates, the first to second string units in one of theblocks are arranged to be separated from each other in the seconddirection, the first string unit includes a first source-side selecttransistor of the depletion type, and a second source-side selecttransistor of the enhancement type connected in series in order from thememory cell side between a source line and the memory cells of the firststring unit, and the second string unit includes a third source-sideselect transistor of the enhancement type, and a fourth source-sideselect transistor of the depletion type connected in series in orderfrom the memory cell side between the source line and the memory cellsof the second string unit.
 14. A semiconductor memory device,comprising: a first memory string including a first select transistor, afirst memory cell, a second select transistor, and a third selecttransistor connected in series in a first direction; a second memorystring including a fourth select transistor, a second memory cell, afifth select transistor, and a sixth select transistor connected inseries in a first direction; a third memory string including a seventhselect transistor, a third memory cell, an eighth select transistor, anda ninth select transistor connected in series in a first direction; afourth memory string including a tenth select transistor, a fourthmemory cell, a eleventh select transistor, and a twelfth selecttransistor connected in series in a first direction; a first gate lineconnected to a gate of the first select transistor; a second gate lineconnected to a gate of the fourth select transistor; a third gate lineconnected to a gate of the seventh select transistor; and a fourth gateline connected to a gate of the tenth select transistor; the first gateline, the second gate line, the third gate line, and the fourth gateline electrically isolated from each other, the second select transistorbeing a depletion type and the third select transistor being anenhancement type, or the second select transistor being the enhancementtype and the third select transistor being the depletion type, the fifthselect transistor being the depletion type and the sixth selecttransistor being the enhancement type, or the fifth select transistorbeing the enhancement type and the sixth select transistor being thedepletion type, the eighth select transistor being the depletion typeand the ninth select transistor being the enhancement type, or theeighth select transistor being the enhancement type and the ninth selecttransistor being the depletion type, and the eleventh select transistorbeing the depletion type and the twelfth select transistor being theenhancement type, or the eleventh select transistor being theenhancement type and the twelfth select transistor being the depletiontype.
 15. The device according to claim 14, further comprising: a fifthgate line connected to a gate of the second select transistor and a gateof the fifth select transistor; a sixth gate line connected to a gate ofthe eighth select transistor and a gate of the eleventh selecttransistor, different voltages being applied to the fifth gate line andthe sixth gate line; a seventh gate line connected to a gate of thethird select transistor and a gate of the ninth select transistor; andan eighth gate line connected to a gate of the sixth select transistorand a gate of the twelfth select transistor, different voltages beingapplied to the seventh gate line and the eighth gate line.
 16. Thedevice according to claim 15, wherein the fifth gate line and the sixthgate line are substantially parallel along a second directionperpendicular to the first direction, and the seventh gate line and theeighth gate line are substantially parallel along the second direction.17. The device according to claim 15, wherein the first memory stringfurther includes a thirteenth select transistor and a fourteenth selecttransistor connected in series in the first direction, the second memorystring further includes a fifteenth select transistor and a sixteenthselect transistor connected in series in the first direction, the thirdmemory string further includes a seventeenth select transistor and aneighteenth select transistor connected in series in the first direction,the fourth memory string further includes a nineteenth select transistorand a twentieth select transistor connected in series in the firstdirection, and the thirteenth to twentieth select transistors are theenhancement type.
 18. The device according to claim 15, wherein thefirst memory string further includes a thirteenth select transistor anda fourteenth select transistor connected in series in the firstdirection, the second memory string further includes a fifteenth selecttransistor and a sixteenth select transistor connected in series in thefirst direction, the third memory string further includes a seventeenthselect transistor and an eighteenth select transistor connected inseries in the first direction, the fourth memory string further includesa nineteenth select transistor and a twentieth select transistorconnected in series in the first direction, the thirteenth selecttransistor being the depletion type and the fourteenth select transistorbeing the enhancement type, or the thirteenth select transistor beingthe enhancement type and the fourteenth select transistor being thedepletion type, the sixteenth select transistor being the depletion typeand the fifteenth select transistor being the enhancement type, or thesixteenth select transistor being the enhancement type and the fifteenthselect transistor being the depletion type, the seventeenth selecttransistor being the depletion type and the eighteenth select transistorbeing the enhancement type, or the seventeenth select transistor beingthe enhancement type and the eighteenth select transistor being thedepletion type, and the nineteenth select transistor being the depletiontype and the twentieth select transistor being the enhancement type, orthe nineteenth select transistor being the enhancement type and thetwentieth select transistor being the depletion type.
 19. The deviceaccording to claim 18, wherein two of the second select transistor, thethird select transistor, the thirteenth select transistor, and thefourteenth select transistor are the depletion type, and another two arethe enhancement type, two of the fifth select transistor, the sixthselect transistor, the fifteen select transistor, and the sixteenthselect transistor are the depletion type, and another two are theenhancement type, two of the eighth select transistor, the ninth selecttransistor, the seventeen select transistor, and the eighteenth selecttransistor are the depletion type, and another two are the enhancementtype, and two of the eleventh select transistor, the twelfth selecttransistor, the nineteenth select transistor, and the twentieth selecttransistor are the depletion type, and another two are the enhancementtype.